Souhegan Watershed Association

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Water Testing Results
Summer 2010

Souhegan and Merrimack Rivers

George May's Latest Results Summary
Map Showing Test Locations

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, dissolved oxygen, temperature, and bacteria. Weather and streamflow information was also recorded when water samples are collected. Previous results, beginning in 1997, are available in reports that can be found in local libraries. Summaries and original results are available here.

This monitoring program is conducted by trained volunteers who believe in cleaner rivers. Financial support for the program comes from your memberships and donations. If you would like to help continue this monitoring effort, please contact George May at 883-3409 or "georgemay (at) comcast (dot) net" or send a check to SWA, PO Box 1474, Merrimack, NH 03054.

E-Coli Bacteria Counts

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. The results are reported as the number of e-coli bacteria colonies observed under a microscope in 100 ml of water. Bacteria levels below 88 colonies per 100 ml. are considered safe for public swimming areas. Anything above that level may cause ear and eye infections, diarrhea or other gastrointestinal problems in a percentage of swimmers. These bacteria numbers being reported are good for only a few days. They do indicate the general health of the river water at a particular moment in time. The next measurement can be considerably different, depending on water level and temperature, and what has recently washed, flowed, or been poured into the river. The current E-coli results this year are available here.

Dissolved Oxygen Measurements

Dissolved oxygen is "breathed" by fish and insects that live in the water. Dissolved Oxygen requirements for different species vary greatly, even if only fish are considered. One of the more sensitive family groups is trout. The lower limit for them is about 5 mg/L (or 5 ppm). The maximum value attainable is called O2 saturation. The concentration of O2 equal to the saturation limit in water increases with DECREASING temperature and INCREASING pressure. At 1 atmosphere pressure and 20 degrees centigrade the concentration of saturated O2 is 9.1 mg/L, while at 1 atmosphere pressure and 25 degrees centigrade O2 is saturated at 8.2 mg/L. The rate of oxygen usage, the rate of oxygenization (turbulence) and the rate of mixing of the different strata of water all contribute to surface oxygen levels. The simplified conclusion is that adequate oxygen levels indicate a healthy, balanced river habitate.

Cumulative 2010 E-Coli Data

July 20th Report

Water quality monitors for the Merrimack and Souhegan Rivers noticed lots of small fish jumping early Tuesday morning. “The fish were probably looking for more oxygen and trying to cool off.” according to George May, coordinator for the monitoring project. He noted that the dissolved oxygen levels in the water have been declining over the last couple of weeks because of the higher temperatures and lower flows. “This is normal for summer conditions,” he noted, “but the combination makes it a little tougher on the fish. The water temperature right now is higher than the air.”

E. coli levels were also affected by the low flows and higher temperatures. The stretch of the Souhegan River through Wilton, Milford, and Amherst had higher levels than are acceptable for swimming. The program looks for levels under 88 for clean water. The state accepts a higher level up to 126 for swimming holes. None of the sites tested through that stretch met either level. The popular swimming hole on Boston Post Road in Amherst was 261. High E. coli counts can cause intestinal distress and ear and eye infections for swimmers.

The upper stretch of the Souhegan through New Ipswich and Greenville tested very clean; and the lower stretch in Merrimack tested clean.

The Merrimack River between Manchester and Tyngsborough had very mixed results. E, coli levels were very high close to Manchester, A very high reading of 1046 showed up near the railroad bridge at Goffs Falls. The river continued to test high downstream at Depot Street in Merrimack. The reading here was 365. A reading at Greeley Park was 331. “E. coli levels this high are unusual for the Merrimack River,” May noted. “Generally the Merrimack tests very clean unless we have heavy rainstorms and we had no measurable rain for three days prior to the testing,” he said.

The E. coli level near the Tyngsborough Bridge was a very low 8. There has been construction going on right at the water’s edge near the test site that has produced very high counts for the last month. “Apparently the work there is finished and will contribute to low pollution runoff in the future,” he said.

“We’re hoping for more seasonal weather and lower pollution counts for the next test in two weeks,” he said.

The monitoring program is an all volunteer program sponsored by the Souhegan Watershed Association and the Lower Merrimack River Local Advisory Committee. The volunteer coordinator is Karen Mattor. Anyone interested in volunteering to help out can contact her at Lab tests are done by certified technicians at the Milford, Merrimack, Manchester, and Nashua Wastewater Treatment Facilities. More information and past results are available at

The entire length of the Nashua River is tested on a monthly basis by the NRWA. This month’s test was done on Saturday, three days before the tests on the Merrimack and Souhegan. The results for the New Hampshire portion of the Nashua are included here. Except for Walker Brook, a tributary to the Nashua coming out of Greenville and Mason, the E. coli levels were good. The results for the entire length of the Nashua are available on the NRWA website.

July 6th Report

Very hot weather and the lack of rain for the last several holiday days brought out good news for all the swimmers in local rivers. E. coli levels dropped to very acceptable levels at almost all areas along the Souhegan and Merrimack Rivers.

The upper Souhegan River usually tests good. This area is the headwaters section between Ashburnham, MA, and Wilton, NH. The outflow from Billy Ward Pond in Ashburnham was slightly elevated, and the program is looking for corrective measures that can be taken there, but the mainstem of the river was all below the healthy 88 level that the program looks for.

The stretch of the Souhegan between Wilton and the Milford Oval had the highest readings on the river. Readings of 225 were seen in this area. The river quickly recovered however and stayed acceptable until Rte 122 near the Amherst Country Club. Readings here increased back over the 88 level and stayed high till the Amherst Canoeport at Boston Post Road, a popular swimming hole. Downstream the levels dropped to acceptable levels the rest of the way to the Merrimack River. Generally readings were quite good according to George May, SWA president and sponsor of the monitoring program. “Although a couple of spots were higher than 88, the river is pretty clean and I wouldn’t hesitate to swim in any of the popular spots,” he said.

The Merrimack River also tested very good according to May. “With the exception of one site near the Tyngsborough Bridge, the Merrimack looks pretty clean for E. coli. That site has construction going on there and they are working right on the water’s edge. Hopefully the work they are doing will prevent pollution in the future, but right now it’s a mess,” he said. The E. coli count here was an extremely high 517.

The hot weather and lack of rain also reduced the rivers’ flow. Both rivers are considerably below their historical average for this time of year. The lower level also exposed interesting things for the monitors when they checked their sites. In Greenville near the power line across the Souhegan the monitor removed a half bag of cement that someone had disposed of in the river. Unfortunately monitors have to clean up trash at their sites.

Not all of it is intentional. One of the monitors picked up a wallet that had been dropped – probably by a fisherman - and turned it in to the Milford Police.

Besides people coming to the river, lots of insects were noted on and along the rivers. These attracted lots of fish, frogs, and birds that were also spotted by the monitors.

The monitoring program is an all volunteer program sponsored by the Souhegan Watershed Association and the Lower Merrimack River Local Advisory Committee. The volunteer coordinator is Karen Mattor. Anyone interested in volunteering to help out can contact her at Lab tests are done by certified technicians at the Milford, Merrimack, Manchester, and Nashua Wastewater Treatment Facilities. More information and past results are available at

June 22nd Report

Water quality monitors on the Souhegan and Merrimack Rivers noted all kinds of summer activities on the first full day of summer. Swimmers, boaters, fishermen were all noted early Tuesday morning. Monitors noted that the water temperatures were higher than the air temperatures around 8am that morning. And many noted lots of small salmon fry at their test sites along the Souhegan. A couple of larger fish were also noted trying to get through the very shallow water coming into the Souhegan from the Merrimack River. Birds of all types were flying around.

Unfortunately a few monitors also reported an oily sheen on the water, slight septic smells in a couple of locations, and a possible area of milfoil near the Tyngsborough Bridge.

E. coli results were mixed. The Merrimack River between Manchester and Tyngsborough had very low bacteria counts with one exception near the Tyngsborough Bridge. The count there tied for the worst this week - seen just upstream of the Milford Oval on the Souhegan. The Merrimack River may have been an aberration; the high count on the Souhegan was not.

The upper section of the Souhegan from New Ipswich through Wilton had very good results, but from Milford through Amherst the E. coli counts generally increased to unacceptable levels. The highest count, 326, was seen near the Souhegan Valley Boys and Girls Club just upstream of the Milford Oval. This section of the river usually has higher counts than the upstream section because of its warmer, sandy, shallow, slow-moving nature. The monitoring program uses 88 as the acceptable E. coli level; levels higher than this can cause swimmer’s itch, eye and ear infections, and diarrhea in some people. Levels higher than 88 cause a public swimming beach to be closed until levels decrease. There are no public swimming areas on either river; however, there are several places frequently used by swimmers. A couple of these had higher than 88 counts – the Amherst Canoeport on Boston Post Road tested at 194 and Turkey Hill Bridge tested at 145. The Horseshoe in Wilton was a very acceptable 18.

All of the dissolved oxygen levels on both rivers came in as very good. Most all were in the 8-9 range. Dissolved oxygen is needed for healthy fish who get their oxygen from the water. Volunteer monitors also note air and water temperatures and various observations at the 20 sites along the entire length of the Souhegan and 11 sites along the Merrimack every other Tuesday morning through September. The lab testing is performed by certified personnel at the Milford, Merrimack, and Nashua Wastewater Treatment Facilities. There are still openings for anyone who would like to volunteer to join the program. Information and past results are available on the Souhegan River website.

June 8th Report

Water quality monitoring on the Souhegan and Merrimack Rivers began for the 14th consecutive year last Tuesday morning. Dozens of volunteer monitors fanned out over the length of the Souhegan River from Ashburnham, MA, to Merrimack, NH, and over the stretch of the Merrimack between Manchester and Tyngsborough to take samples to be analyzed for dissolved oxygen and E. coli bacteria at the Milford, Merrimack, and Nashua wastewater treatment plants. The same tests will be repeated every other Tuesday morning through September.

“What was found was approximately what I expected,” said George May, president of the Souhegan Watershed Association. “All of the E. coli counts are too high and all of the dissolved oxygen counts are excellent.” Heavy rains after a very dry, hot spell washed lots of bacteria off the banks and into the rivers and these same heavy rainstorms increased the river flow and splashed in lots of oxygen, he explained.

The Souhegan River was more impacted than the Merrimack because of its smaller size. E. coli counts on the Souhegan ranged from marginally acceptable in the upper river, between New Ipswich and Wilton, to completely unacceptable on the lower stretch, between Milford and Merrimack. The acceptable level of E. coli for this test is 88. Any number higher than 88 would require public swimming areas to be closed. The lower Souhegan was in the 500-600 range.

The Merrimack River tested much better than the Souhegan because of its size, but the river still tested in the 100-150 range, much higher than the acceptable level. Water testing higher than the 88 level can produce intestinal ailments, eye and ear infections, and other swimmers’ complaints.

“Swimming at these levels is not a good idea,” said Karen Mattor, volunteer coordinator for the program, “but with the couple of dry or only drizzly days since Tuesday morning, the levels have probably dropped.” The bacteria have a short lifespan of about three days so improved weather conditions can clear the rivers up fairly quickly, she explained.

Water flow on both rivers was way below average until storms dumped lots of rain over the weekend. The flow shot straight up until the time of the testing on Tuesday morning. The Souhegan was almost double its historic average for this date. The upper stretch was running at 90 cubic feet per second and the lower stretch as measured in Merrimack was at 203 cfs. The Merrimack River was running at 4340 cfs. Its historic average is 3610 for this time.

One cubic foot per second translates to 7 ½ gallons; that means that while you are standing admiring the view along the Merrimack River for five minutes, almost 10 million gallons have flowed by.

Generally speaking both rivers have cleaned up a lot since testing first began 14 years ago, according to May. Today both rivers are relatively clean. It’s only after heavy rains that bacteria levels are too high for swimming, fishing and boating.

The next test will be done on June 22; the results will be available one or two days later.

Test results from past years are also shown on the SWA website at

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