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2000 Souhegan E-coli results
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1999 Souhegan E-coli results
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1998 Souhegan E-coli results
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Stream Flow Measurements

Souhegan River Water Testing Results
Summer 2000

The Souhegan Watershed Association monitors the entire length of the Souhegan River and part of the Merrimack River for their aquatic health. Water samples are tested for pH, phosphorus, disolved oxygen, temperature, and bacteria. Weather and streamflow information was also recorded when water samples are collected.

Previous results for 1997, 1998, and 1999 results are available in a report that can be found in local libraries. Summaries are available here. The current E-coli results this year are available here.

This monitoring program is conducted by trained volunteers who believe in cleaner rivers. Financial support for the program comes from a grant from NHDES and local conservation commissions. Our E-coli samples are prepared and counted by professionals at the local wastewater treatment plants in Greenville, Merrimack, Milford, and Nashua on a volunteer basis. If you would like to help continue this monitoring effort, please contact George May at 883-3409 or

September 21st results

The Souhegan Watershed Association retested five sites along the river in Milford and Amherst on Thursday, September 21, and pronounced the river in acceptable shape.

On Tuesday, September 19, the SWA conducted what was to be the final water quality test of the year on the Souhegan and Merrimack Rivers. The SWA has done 8 biweekly tests on a total of 26 sites on both rivers since the beginning of June. But the test showed several surprising, abnormal E.coli readings on the Souhegan. A dangerously high E.coli count was recorded in the area just downstream of Milford center. The SWA looks for a reading of 88 or lower as being acceptable. The reading on Tuesday was 1370.

So volunteers were mobilized once again to retest the area to see if this was a one time pollution discharge or a continuing problem. Luckily the pollution seems to have abated. Tests were taken at Emerson Park, in the center of Milford; downstream at the Swing Bridge; further downstream behind Riverside Cemetery; and further downstream behind Lorden Plaza. The respective E.coli counts were 248, 345, 356, and 350.

"While these results seem high, and indeed are higher than we would like to see, they are more in line with what we would expect," according to Joanne King, coordinator of the SWA water monitoring program. "There was almost an inch of rain less than 24 hours before the second test, and E.coli counts go up nearly everywhere on the river, especially in urban areas, when there’s a heavy rain. Unfortunately, we don’t expect to see swimmable, fishable conditions right in the center of town. These new readings are pretty much in line with what we’ve seen for the last several years," she said.

King noted that this was the second time this year that testing has shown dangerously high spikes in the center of Milford. There was a reading of 1250 discovered on June 27. Retesting a couple of days later again showed that the pollution had been dissipated. “The fact that we only test every two weeks and that we found two spikes in the same area is a cause for concern. Somebody could be dumping waste into the river on the off days, when we are not sampling,” she said. The SWA has indicated that they will notify the Milford Conservation Commission and the Milford Department of Health of their concerns.

The second area that was retested on Thursday was the Amherst Canoeport on Boston Post Road. The Tuesday test showed a reading of 2, but that site has never been below 88 before. Unfortunately, the retest came up with another unacceptable, but expected, reading of 225. The SWA has been trying to find possible causes for consistently high readings throughout the Souhegan in Amherst but has not been able to find any manmade causes. Two of the SWA volunteers canoed this stretch of the river last week but found no clear evidence of human induced pollution sources. “Our present thinking is that the high readings are natural. The river slows down, the soil is sandy, and there are otters, muskrats and a lot of birds and wild animals nesting in the high banks that may be causing the elevated readings,” said King.

The SWA has tested the Souhegan and Merrimack for the last several years and pending funding, expects to continue its testing program again next year. All of the testing is performed by trained volunteers. If you would like to support SWA with a corporate, family or individual membership or become a volunteer for the testing program, contact George May at 883-3409.

September 19th results

The final test for E.coli bacteria on the Merrimack and Souhegan Rivers for this season produced a couple of abnormal readings on the Souhegan River.

Except for this, both rivers showed generally good results. The Merrimack especially has had low bacteria readings almost all summer and the biweekly test taken on Tuesday, September 19, continued this pattern of low E.coli counts. The Merrimack has 26 Combined Sewer Overflows (CSOs) in Manchester and 9 in Nashua. After substantial rainstorms the stormdrain runoff is diverted from the sewage treatment plants and goes untreated into the river. However, except after rainstorms the Merrimack is relatively free of E.coli bacteria.

The Souhegan had three surprises – one good and two bad. The first reading just downstream of the center of Milford showed very high bacteria levels, the highest seen anyplace all season. A reading of 1370 colonies exceeds even a scare earlier in the season when Emerson Park shot up to 1250. That scare in June sent town officials out to take additional tests to confirm that the bacteria count went down a couple of days later. According to Joanne King, monitoring coordinator for SWA, “The fact that we have not one but two consecutive sites whose counts have skyrocketed from the norm this time indicates that there is a pollution discharge coming from a single point. Unfortunately we do not have data for downtown Milford that may have enabled us to better pinpoint the source. Any time we see counts this high, we do follow up tests, in this case in the downtown area as well as downstream, to try and get some answers. It looks as though somebody discharged waste directly to the river shortly before the tests were taken.

Monitors will take the follow up tests on Thursday; the results should be available on Friday and will be reported as soon as they’re available.

The second surprise was the reading at the Horseshoe, a well-known swimming hole in Wilton. The reading here was 270, well above the very low levels experienced all season. The monitor at this site reported that a landowner had dumped debris and burned logs along the river since the last test two weeks ago. The Horseshoe has had very low bacteria counts not only this season but also last season.

The third surprise was a good one. The Amherst Canoe port on Boston Post Road near Souhegan High School had been a popular swimming spot until last year when the town posted it for no swimming because of the high bacteria counts. For the last several years bacteria counts have consistently remained way above the 88 count considered acceptable for public swimming areas. This week’s test is the very first ever showing an acceptable reading. It was 2.

SWA monitors canoed the Milford-Amherst section of the Souhegan recently looking unsuccessfully for causes of the high E.coli counts that have consistently plagued this stretch of the river. A preliminary conclusion is that the bacteria is predominately naturally occurring caused by a good deal of in-stream animal activity in the area . Beaver Brook comes through the center of Amherst and has been looked at as contributing to the problem. A special test taken from Beaver Brook showed a level of 200, higher than acceptable but not unexpected by the monitors. A test taken slightly downstream in the Souhegan itself showed a similar reading at 180.

The Souhegan Watershed Association and the Lower Merrimack River Local Advisory Committee have performed these biweekly tests for the last several years to determine the health of the rivers and to establish patterns that may indicate possible places for remediation. One of the tests that the volunteers perform is for E.coli bacteria, which indicates how healthy the water is for humans. Levels above 88 may cause ear and eye infections, diarrhea or other gastrointestinal problems among some people swimming in the river.

A full report of the season’s testing will be compiled by the end of the year. The report will be distributed to all watershed conservation commissions and town libraries and is available to anyone interested. Reports and comparisons from prior years are already available at town libraries.

September 5th results

The bacteria levels in both the Merrimack and Souhegan Rivers have changed only slightly since they were tested two weeks ago. They were good then and they are good now according to volunteers from the Souhegan Watershed Association and the Lower Merrimack River Local Advisory Committee who perform the biweekly tests.

The organizations do a series of tests to determine the health of the rivers and to establish trends over the season, and one of the tests – for E. Coli bacteria - indicates how healthy the water is for humans. The SWA uses the state standard for public swimming areas as a conservative baseline. E. Coli bacteria levels above 88 are unacceptable because they may cause ear and eye infections, diarrhea or other gastrointestinal problems among some of the swimmers.

The Merrimack River from the Manchester line to Tyngsboro again had very low bacteria counts this week. The uppermost site near the railroad bridge at Goffs Falls had no detectable bacteria at all. This is the second time this season that site had no bacteria. There was a slightly above acceptable reading at the Tayors Falls Bridge on Canal Street in Nashua, but that was the only reading above 88 for the entire river. Generally the Merrimack River is quite clean.

The Souhegan River was well below the 88 baseline except for the stretch between downtown Milford and the Boston Post Road bridge in Amherst. Generally the stretch in downtown Milford would be expected to have high counts because of the population density there and this week’s test was no exception. But there was a spike to 480 behind Lorden Plaza in Milford that may be attributable to the Milford Wastewater Treatment Plant. This particular site is a downstream bracket for the wastewater treatment plant. The reading went from 320 above the plant to 480 below it. This site has not been a problem in the past and wastewater treatment plants usually release effluent that is cleaner than the river its released to. The Merrimack Wastewater Treatment Plant, for example, had a reading of 13 for their effluent this week. The bracketing at the Greenville Wastewater Treatment Plant on the Souhegan showed no increase, but that plant is being rebuilt to bring it up to more acceptable standards. There have been problems there in the past.

The stretch of the Souhegan through Greenville showed little cause for concern this week. Again downtown areas usually have higher counts, but not this time. The counts have come down to acceptable levels since the beginning of August, perhaps because of the lack of rain that was so pervasive earlier in the season. The flow level of the Souhegan has also moderated in the last few weeks. The flow was right at its historical average for this time of the year when these tests were taken. It has been higher than average for most of this season. The flow on Tuesday was 65 CFS (cubic feet per second) measured above Wildcat Falls in Merrimack.

The following are the bacteria results for all of the sites tested this week. All of the bacteria results from this year and last are available on the SWA website at The entire report on the overall chemical health of the rivers for the last several years is available at all watershed libraries.

The next test will be done on September 19 and will be the last test for this season.

August 22nd results

E. Coli bacteria tests performed on 25 sites on the Souhegan and Merrimack Rivers on August 22 by volunteers for the Souhegan Watershed Association and Merrimack River Local Advisory Committee indicate little concern for human safety for boaters, swimmers, bathers, waders, fishermen, or others in contact with either river.

"This latest test gives us some of the best results we’ve had all year," according to George May, secretary of the SWA. "Except for the stretch of the Souhegan from the center of Milford through Amherst not a single site on either river had a reading above 88."

The SWA uses 88 E. Coli colonies per 100 milliliters of water as a conservative benchmark. This is the state standard for public swimming areas. Above this level some swimmers may experience ear and eye infections, diarrhea or other gastrointestinal problems. Volunteers monitor the rivers every two weeks during the summer.

"Two sites in Amherst were missed in this go-round, but both have exceeded the 88 level on each of the five tests so far this season, so it’s safe to assume that they would have exceeded the level again this week," said May. "For some reason that we have not yet figured out the levels through Amherst are always high. This has been true since we started collecting data several years ago."

The Merrimack River has had excellent results all season and continues to show excellent results this week. The highest level between Manchester and Tyngsboro was 50, well below the 88 level of concern. "The only time the Merrimack has shown high E. Coli readings has been after heavy rainstorms when the wastewater treatment plants were overwhelmed by stormwater runoff that goes into the single sewer pipes (CSOs)," said May.

There are no CSOs on the Souhegan River, but there are 26 on the Merrimack in Manchester and 9 in Nashua. Both cities are in the process of replacing their single pipe systems with separate pipes for sewer and stormwater runoff, but the process will take 20 years to complete.

The SWA has done some drain stenciling in Merrimack and in Milford to remind people that many storm drains go directly to the river and that excess lawn fertilizer that goes into the drains will pollute the river and kill the fish. The SWA has also sponsored a number of schools along the Souhegan and Merrimack in raising baby salmon in their classrooms in order to increase an awareness of the rivers. Children in New Ipswich, Wilton, Milford, Amherst, Merrimack, Nashua and Litchfield are all part of the US Fish & Wildlife Adopt a Salmon Family. The Souhegan is the premier river in this area for releasing salmon fry in order to reestablish salmon in the Merrimack Watershed.

The Souhegan River has also just recently been included in the state Rivers Management & Protection Program. The Merrimack has been included in the state program for the last ten years, since the program’s inception.

August 8th results

Tests performed on the Souhegan and Merrimack Rivers on August 8 indicate little change in bacteria counts since the last tests two weeks ago. "We have some mixed results this week, but generally bacteria levels are remaining steady right now," according to George May, a volunteer monitor for the Souhegan Watershed Association and Merrimack River Local Advisory Committee.

"We have very mixed results for the Merrimack River, but find it difficult to account for spikes in the bacteria counts at Thorntons Ferry in Merrimack and Greeley Park in Nashua. We’ve had very good tests on the Merrimack all season and so these may be aberrations. We had only five tests on the Merrimack this week, so we don’t have complete data. The volunteer monitor at Greeley Park noted a rusty flow on the left of the boat ramp that may account for that jump," said May. The Greeley Park boat ramp tested at 730 E. Coli colonies per 100 milliliters of water, up from 70 two weeks ago. Thorntons Ferry jumped to 382 from 40 two weeks ago.

Bacteria levels above 88 are considered unsafe for public swimming areas because they may cause ear and eye infections, diarrhea or other gastrointestinal problems among some of the swimmers.

May noted that Dissolved Oxygen levels in both rivers has been very good, especially compared to last year. The constant rains that we’ve had this year has brought oxygen into the rivers and kept the river levels up and temperatures down. Last year one could walk across the Souhegan in many places; this week the Souhegan was flowing at almost double its historic average. DO levels are crucial for cold water fish like the salmon and trout in the Souhegan River.

July 25th results

E. Coli bacteria levels on the Souhegan and Merrimack Rivers returned to a more normal level on tests taken by volunteers from the Souhegan Watershed Association and Merrimack River Local Advisory Committee, according to George May, secretary of the SWA.

Tests taken two weeks ago were taken after a substantial rainfall and the bacteria counts were extremely high. The recent test taken on Tuesday, July 25, came after several days of warm, dry weather. "Since we’re seeing bacteria counts on the Souhegan increase substantially after rainstorms, it shows that pollution is being washed into the river from roads, parking lots, and other developed areas," according to Joanne King, coordinator for the monitoring project. "It’s good," she said, to have data from both extremely wet and extremely dry conditions to be able to determine where the pollution is coming from. And if we can see where it’s coming from, we can go to work on fixing the problem. As the population in this area of New Hampshire continues to grow, there’s more consumption of resources and more waste production. We can’t stop the growth in our area but we can stay educated and come up with creative solutions to protecting our local resources."

"The Souhegan River seems clean enough by itself, but when we have rain, pollution levels go up, which seems to indicate bacteria and other pollutants such as gasoline, oil, pesticides or herbicides are being washed into the river. Storm drains all along the Souhegan must be suspected of introducing pollution," she said. "When we look at the number of storm drains that drain directly to the river, as we have through drain stenciling programs, we find a good correlation between the number of drains and the levels of pollution in these river segments during storm events."

"The present rains that we’re experiencing are probably bringing bacteria levels back up to unhealthy levels," she said. "Swimming in the Souhegan right now probably wouldn’t be a good idea." Bacteria levels below 88 are considered completely safe for swimming areas. Above 88 some swimmers may experience ear and eye infections, diarrhea or other gastrointestinal problems. This is the level SWA uses as a guide.

The popular swimming hole at Boston Post Road near Souhegan High School decreased to a count of 120, still slightly above the level preferred by the SWA, but it came down from 600 in the prior test and to its lowest level in more than a year. The swimming hole called The Horseshoe in Wilton continued to be well within the acceptable range. It has not been above 88 all year.

Emerson Park near the Oval in Milford measured at only 70. This spot was the site of a scare last month when the E. Coli level shot up to 1250 and required additional testing several days later to confirm that the bacteria levels were tolerable.

The Swing Bridge site in downtown Milford continues to have high counts despite the dry weather, indicating that the source of pollution is instream rather than from runoff. Low flow caused by the dam in combination with a large population of well-fed waterfowl are most likely the source.

The Merrimack River continued to show very low E. Coli counts indicating how clean the Merrimack has become over the last several years. Prior to the passage of the Clean Water Act twenty-five years ago the Merrimack was on the list of the ten dirtiest rivers in the country. There are still CSOs dumping raw sewage into the Merrimack in Manchester and Nashua after heavy rainstorms . But other than that the bacteria counts all along the Merrimack are always very low.

July 11th results

"The high E. coli bacteria counts on July 11th are probably the result of a significant rainstorm twenty four hours before our sampling date," according to Joanne King, coordinator of the volunteer water quality monitoring project of the Souhegan Watershed Association (SWA) and Merrimack River Local Advisory Committee (LMRLAC), the organizations responsible for testing on the two rivers.

"The flow on the Souhegan doubled from 80 cubic feet per second (CFS) to 170 CFS within the twenty-four hours before the test, and we sampled at its peak flow," according to George May, secretary of the SWA and one of the volunteer monitors. "During periods of heavy rain bacteria are washed into the rivers and streams from all kinds of sources. It’s during heavy rains that we experience our worst E. coli readings. Chances are that bacteria levels have gone down by now since we haven’t had a lot of rain since the test," said May.

Interestingly, the bacteria level at The Horseshoe, a popular swimming spot in Wilton, was 70, well within the limits that the SWA likes to see. Bacteria levels below 88 are considered completely safe for public swimming areas. Higher levels may cause ear and eye infections, diarrhea or other gastrointestinal problems among some of the swimmers. The Horseshoe was one of only three sites on the entire length of the Souhegan that passed the biweekly test.

The popular swimming hole at Boston Post Road near Souhegan High School had two readings taken. One exceeded 800 and the other 590. This site has not passed any tests for the last couple of years and the town has posted no swimming signs.

"Testing under all conditions gives us a pretty good picture of the river under all conditions, said King. "However, when, after a heavy rainfall, we are seeing bacteria counts on the Souhegan River that are approaching the counts seen at the Combined Sewer Overflows (CSOs) on the Merimack and Nashua Rivers, it's a good indication that we need to be more mindful of our land uses along the river."

"These high counts that we are seeing from runoff after a storm event are not from ‘naturally occurring’ sources but from the way we use the land. People could help keep the counts down in a number of ways:

  1. Don't feed and encourage ducks, geese and pigeons
  2. Maintain septic systems with an inspection and pumping every 2-3 years
  3. Pick up pet waste in yards and on trails
  4. Keep livestock manure cleaned up and away from river or catch basins
  5. Maintain a vegetative buffer between lawns and river
  6. Be aware of storm drains whose outfall is on the river and protect what goes into them. Storm drain systems enable pollutants far from the river’s edge to enter the river," said King.

June 27th results

Water quality testing being done by the Souhegan Watershed Association (SWA) shows several areas of the Souhegan River where E. Coli bacteria counts have risen since tests performed two weeks ago. George May, one of the volunteers performing the tests, said that the frequent and steady rains over the last couple of weeks may be washing pollution into the river and causing the increase in bacteria. Of the sixteen sites tested along the entire length of the river only three tested at acceptable levels. All of the rest exceeded the 88 count considered the safety cutoff for public swimming areas.

Three sites in Greenville have increased in bacteria levels. All three sites exceeded 200 colonies per 100 milliliter, more than double the levels of two weeks ago. "There is very little vegetative buffer to cut any pollution flowing toward the river as the river flows along Rte 123. But we’re interested in finding human causes of the pollution source," said May. "There have been spikes in the levels in this area in the past."

Most disturbingly, the E. Coli reading taken at Emerson Park next to the Milford Oval leaped to 1250, the highest reading the SWA has ever recorded in the four years they’ve been testing the river. "Something happened here to cause this kind of jump. It may be a fluke reading, but officials in Milford have been notified and are looking for the problem," said May.

The bacteria levels stayed above 88 all the way from Milford to the mouth of the river. Finally the bacteria level dropped to 14 at the test site between the Everett Turnpike and Rte 3 in Merrimack. This site, the popular swimming hole at the Horseshoe in Wilton, and Highbridge in New Ipswich were the only sites along the entire length of the river to test positively. All the others had unacceptable bacteria contamination.

The Merrimack River is tested at nine sites between Manchester and Tyngsboro through the Merrimack River Local Advisory Committee (LMRLAC). "Generally speaking the Merrimack River is quite clean," said May. "There may be other pollution problems, but bacteria is not among them. Two weeks ago the site at Goffs Falls at the railroad bridge on the Litchfield/Manchester border tested at 0. This week it was 30. Those are excellent numbers," he said.

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