BRATTLEBORO -- Dry weather likely is driving down the level of potentially harmful E. coli bacteria in area rivers, a monitoring group reported Friday.
In contrast with earlier tests, the latest sampling by Southeastern Vermont Watershed Alliance shows relatively low levels of E. coli in seven waterways.
Also in contrast with previous testing, these samples were not preceded by heavy rainfall that can wash large amounts of the bacteria into streams.
"No rain and no runoff mostly explains the effect," Laurie Callahan, the alliance's water quality monitoring program coordinator, wrote in a note accompanying test results.
The alliance began its monitoring program June 13 and found that 11 of 17 tested sites exceeded governmental "safe swimming" standards of 235 E. coli per 100 milliliters of water.
The next round of samples, collected June 27, showed 11 of 19 sites exceeding that standard. Two spots -- both on the Williams River -- have E. coli levels too high to be measured.
That prompted concern. E. coli is found in fecal matter, and it can cause illnesses including diarrhea, urinary-tract infections and respiratory problems.
Samples collected Wednesday, however, produced a much-improved result. Only four of 22 tested sites had E. coli levels that were above the safe-swimming limit:
-- Whetstone Brook behind Brattleboro Food Co-op registered an E. coli level of 326.
-- Also at 326 was the Middle
-- Saxtons River at the Bellows Falls/Westminster sandy beach produced an E. coli count of 286. But a second test of the same site showed a score of 194, putting it within safe-swimming standards.
-- Williams River at Chester below Missing Link Road bridge came in at 276.
Those levels were tame in comparison with the alliance's first two tests, which showed some sites hosting E. coli counts into the thousands. In the June 13 sample, for instance, the same Whetstone site produced a 1,987 E. coli count.
The biggest improvement came on Williams River, where four of five testing sites were out of compliance on June 27. Wednesday's samples showed four of the five with safe-for-swimming bacterial levels.
Also improving since June 27 was Saxtons River, where two of the three monitoring sites had acceptable E. coli counts on Wednesday.
The West River was a relatively clean waterway in June 27 testing, as only three of eight sites showed too many E. coli for safe swimming. On Wednesday, it was even cleaner: All eight West River sites were considered safe, and none scored above 109.
Though the area has been dry recently, Callahan reiterated a warning about the relationship between rain and E. coli.
"Common sense dictates that swimming and/or boating should be avoided until the water quality improves, typically 24-48 hours after significant rainfall," she said.
A full report will be posted on the alliance's website, https://sites.google.com/site/vtsevwa.
Alliance leaders have said they need funding and volunteer assistance in order to continue their programs.
Callahan said the group's monitoring initiative is supported by Vermont Department of Environmental Conservation's LaRosa Environmental Laboratory partnership program, Connecticut River Watershed Council and Green Mountain Coffee Roasters along with municipalities, alliance members and more than 20 volunteers.
In other local E. coli testing, volunteers on Wednesday found bacterial levels that are safe for swimming and boating at the Putney Rowing Club docks on the Connecticut River in Putney. Safe levels also were found there on June 27 and June 13.
More E. coli-monitoring data for the Connecticut is available at www.connecticutriver.us.
Mike Faher can be reached at email@example.com or 802-254-2311, ext. 275.