The Souhegan Water­shed Association volun­teers found better than expected water quality in the local rivers this week. The Merrimack River be­tween Manchester and Tyngsborough continues to have low, excellent E. coli levels. And this has been true all summer. Be­cause of its size, the Mer­rimack River usually tests good; it’s only after big rainstorms that the E. coli levels increase beyond the acceptable range.

The Souhegan River is a much smaller river and so is more influenced by E. coli bacteria. Typically stretches where the river meanders slowly back and forth and through population centers the E. coli levels are raised to unacceptable levels. And that’s what the tests found this week. Downtown sec­tions through Greenville, Wilton, and Milford had readings higher than ac­ceptable. The downtown section in Wilton had the worst level seen this week – 461. This would be a dangerous level for swim­ming.

The stretch through downtown Milford was still above acceptable, but much lower than ex­pected and much lower than two weeks ago – the test at the Swing Bridge was 166. But none of these places are known for bathing.

The E. coli levels at swimming spots is what’s important with all this hot weather. And the good news is that all the swim­ming spots tested good this week. Watson Park in Merrimack continues to have excellent results. Although SWA monitors every two weeks, this site is monitored every week and the results are posted at the park. The results here have been good for the last few weeks. The Horseshoe in Wilton had the highest number this week, but at 60 this is still considered excellent. Generally the E. coli num­bers this week are consid­ered quite good, better than expected.

Numbers less than 88 are excellent. Numbers higher than 126 are not ac­ceptable for swimming.

Both rivers continued to have very low flows due to the lack of rain. The Souhegan has been running below its histori­cal average all summer – the last time there was normal flow was back in March. Flow today should be almost twice as much just to get back to normal. These low flows mean that any pollution getting into the rivers has little to di­lute it. The Merrimack is a much larger river and flow is largely controlled by upstream and down­stream dams so the effects of pollution are not as great.

The dissolved oxygen levels are still running at an acceptable level. The dissolved oxygen levels determine the health of the river for the fish and other river animals. Both rivers have historically done very well and con­tinue at very acceptable levels. The actual read­ings and explanations for DO and other tests is list­ed at www.souheganriver. org. Past years’ readings are also listed there.

The rivers will be test­ed again every two weeks during the summer. Thir­ty volunteers, many of whom have been with the program for many years, adopt a site and test ev­ery other Tuesday morn­ing and carry the samples to the local wastewa­ter treatment plants in Greenville, Milford, Mer­rimack, Manchester and Nashua where the sam­ples are processed by licensed professionals. There are still sites avail­able and new volunteers are always welcome; sites with NA are open right now. More information is available on the SWA website.

The next test will be on July 26.