Souhegan Watershed Association

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2012 E-coli results
2010 Testing Results
2009 Testing Results
2009 E-coli results
2008 Testing Results
2008 E-coli results
2007 Testing Results
2007 E-coli results
2006 Testing Results
2006 E-coli results
2005 Testing Results
2005 E-coli results
2004 Testing Results
2004 E-coli results
2003 Testing Results
2003 E-coli results
2002 Testing Results
2002 E-coli results
2001 Testing Results
2001 DO results
2001 E-coli results
2000 Testing Results
2000 E-coli results
1999 Testing Results
1999 E-coli results
1998 Testing Results
1998 E-coli results
1997 E-coli results
Stream Flow Measurements

Water Testing Results

Souhegan and Merrimack Rivers

Map Showing Test Locations

The Souhegan Watershed Association monitors the entire length of the Souhegan River and the section of the Merrimack River between Manchester and Tyngsborough for their aquatic health. Water samples are tested for dissolved oxygen, temperature, turbidity, and bacteria. Occasionally also for pH and phosphorus as needed. Weather and streamflow information is 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.

Heavy metal testing and macroinvertibrate testing has also been done on occasion in the past

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

This test shows how healthy the water is for human use

Our E-coli samples are prepared and counted by professionals at the local wastewater treatment plants in Greenville, Manchester, Merrimack, Milford, and Nashua on a volunteer basis. The results are reported as the number of e-coli bacteria colonies observed 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. Levels between 88 and 126 are suitable for healthy adults. We don't recommend swimming between 126 and 406. Levels above 406 are dangerous and should be avoided. 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 below.They are generally available the day after the test. The test takes 24 hours.

Dissolved Oxygen Measurements

This test shows the general health of the river itself

Dissolved oxygen is "breathed" by fish and insects that live in the water. Besides occuring naturally (H2O), turbulence over rocks and rainstorms increases DO levels. Interestingly, rainstorms that can increase E.coli levels, which is bad for humans, increases DO levels, which is good for fish. 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). We never expect to see levels this low in either the Souhegan or Merrimack.

The simplified conclusion is that adequate oxygen levels indicate a healthy, balanced river habitat.

  • 2019: June 11, June 25, July 9, July 23, August 6, August 20, 2019 Year-End Report,

  • 2018: June 12, June 26, July 10, July 24, August 7, August 21, 2018 Year-End Report,

  • 2017: June 13, June 27, July 11, July 25, August 8, August 22, 2017 Year-End Report,

  • 2016: June 14, June 28, July 12, July 26, August 9, August 23, 2016 Year-End Report,

  • 2015: June 2, June 16, June 30, July 14, July 28, August 11, August 25, September 8,

  • 2014: June 3, June 17, July 1, July 15, July 29, August 12, August 26, September 9,

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