Water Quality Testing Results
Overview
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, macroinvertibrate testing, and DNA 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 consider joining or donating to the SWA.
Heavy metal testing, macroinvertibrate testing, and DNA 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 consider joining or donating to the SWA.
Results
Results for 2022 will be published as soon as they are available and are listed below:
They are also published on our Facebook page
- June 21, 2022
- July 5, 2022
- July 19, 2022
- August 2, 2022
- August 16, 2022
- August 30, 2022
Results from 2021 monitoring are available below:
- June 29, 2021 (pdf | word)
- July 27, 2021 (pdf | word)
- August 31, 2021 (pdf | word)
Results from previous years are available here.
Unfortunately, due to the COVID-19 pandemic, monitoring was not conducted during 2020.
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.
It should be noted that E-coli levels generally rise after a rainstorm - and especially after a rainstorm preceeded by prolonged dry weather.
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.
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.