Drains increase E. coli in rivers

Water quality monitors had to go out in drizzly rain and negotiate slippery rocks on Tuesday, July 11, to collect river samples last week. What they found were moderately high E. coli counts in the downtown sections of Wilton and Milford, where storm drains were draining runoff into the Souhegan River.

E. coli levels remained high through Milford and Amherst, but moderated to acceptable levels in Merrimack. The popular swimming spot at Watson Park in Merrimack was an acceptable level of 88. All of the other spots where people swim were also acceptable with the exception of the Boston Post Road Canoeport in Amherst. The level there usually tests high, and last week was no exception – the level was 225, higher than an acceptable level for swimming.

An unusual leap in E. coli to dangerous levels was recorded downstream of Kaley Park in Milford. This appears to have been caused by a singular event, and the program is investigating.

All of the Souhegan River upstream of Wilton had excellent E. coli levels. That is almost always the case.

E. coli levels below 88 are completely safe for swimming; below 126 is OK for most people, but small children or those with compromised immune systems may experience gastrointestinal problems and swimmer’s eye or ear. Higher than 126 isn’t recommended, and higher than 406 is dangerous.

The Merrimack River between Manchester and Tyngsborough, Mass., had acceptable E. coli levels all the way with one exception. The test site just below where the Souhegan River empties in showed the effects of that river’s higher counts.

The level here increased to 114 from surrounding levels that were half that. However, the larger river quickly absorbed and diluted that pollution and returned to excellent E. coli levels all the way to Tyngsborough. The Merrimack River typically has excellent E. coli levels.

Dissolved oxygen levels are also tested. This test is a better indicator of the general health of the river. Worsening dissolved oxygen showed up in the lower stretch of the river upstream of Tyngsborough. Up to this point in the summer, DO levels were above 8, an excellent level. Last week, a couple of the sites tested in the 6-7 range, which bears watching, and may be because of refilling the dam in Lowell, Mass.

The Souhegan River had excellent DO levels throughout its length.

Souhegan Watershed Association monitors also reported lots of animals, bugs and birds out along the rivers – great blue herons, especially, were seen at several sites on the Merrimack and Souhegan rivers.

The rivers will be tested again on Tuesday, July 25. Thirty volunteers, many of whom have been with the program for many years, adopt a site and test every other Tuesday morning. They take the samples to wastewater treatment plants in Greenville, Milford, Merrimack, Manchester or Nashua, where the samples are processed by certified professionals.

Additional volunteers are always welcome.

For more information, visit www.souheganriver.org.

– Submitted by

Souhegan Watershed Association

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