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Nashua;58.0;http://forecast.weather.gov/images/wtf/small/ovc.png;2014-09-30 17:52:24
Saturday, July 19, 2014

Heavy rains may raise E. coli levels in rivers

By the time you read this, the E. coli samples taken on Tuesday morning may be invalid. The Souhegan Watershed Association monitors the Souhegan and Merrimack Rivers every other Tuesday during the summer. E. coli levels, however, usually rise after heavy rains preceded by dry conditions – and that was the case Wednesday, hours after the sampling session.

Because of the warm weather and desirable swimming conditions, SWA took another sample at Watson Park in Merrimack on Wednesday morning. The results are available at www.souheganriver.org. People frequenting any of the popular swimming spots on either river may want to check for concerns. ...

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By the time you read this, the E. coli samples taken on Tuesday morning may be invalid. The Souhegan Watershed Association monitors the Souhegan and Merrimack Rivers every other Tuesday during the summer. E. coli levels, however, usually rise after heavy rains preceded by dry conditions – and that was the case Wednesday, hours after the sampling session.

Because of the warm weather and desirable swimming conditions, SWA took another sample at Watson Park in Merrimack on Wednesday morning. The results are available at www.souheganriver.org. People frequenting any of the popular swimming spots on either river may want to check for concerns.

Although the heavy rains may worsen the E. coli levels in the rivers, they should improve the dissolved oxygen levels. Higher oxygen levels are better for the river in general. Fish and plants are healthier.

Generally, oxygen levels decrease as the summer heats up and the rivers dry up; rainstorms replace the oxygen.

Dissolved oxygen levels on both rivers has been excellent this season and generally has not been a problem during past monitoring years.

The Tuesday morning E. coli levels were a concern at one swimming hole on the Souhegan. The Amherst Canoeport at Boston Post Road had a level of 325.5. Any level higher than 88 may indicate bacteria that could cause intestinal problems and ear and eye infections, especially among vulnerable swimmers.

Levels between 88 and 126 are satisfactory for most people. Levels above 126 should be avoided. All of the other usual swimming spots on the Souhegan tested at an acceptable level Tuesday.

The upper reaches of the Souhegan from Ashburnham to Wilton had satisfactory readings. Beginning in Downtown Wilton and continuing through Milford and Amherst, the E. coli counts were too high. Over 126.

A dangerous level of 435 was reached at the Swing Bridge near the Oval in Milford. Counts came back down through Merrimack, which has mostly rural riverbanks, to 59 at Watson Park near the mouth of the river.

The Merrimack River from Manchester to Tyngsborough, Mass., tested at an acceptable level throughout its length with one exception of 115 at the Sagamore Bridge.

None of the other sites tested higher than 88.

Both rivers were above average in their flows. Rain since July 4 has been above average and has brought both rivers up. Because the Souhegan is smaller the level was greater. Flows on the Souhegan were roughly double their historic averages for this date.

The Merrimack was flowing about 40 percent higher than its historic average. Wednesday’s rains increased the flows even more.

All of the results can be found at nashuatelegraph.com/specialreportsriver
testresults or souhegan
river.org. The next test will be done on July 29.

Volunteers to help with the monitoring are always welcome and can contact swawatertesting@gmail.com for more information.

The lab tests are all done by certified personnel at the wastewater treatment plants in Manchester, Milford, Nashua and Merrimack.

The program is coordinated by the Souhegan Watershed Association.