Sampling results from the fourth round of Friends of the Mad River’s 2019 Mad River Watch water quality monitoring once again show no sites with unfavorable E. coli levels as of Monday morning, July 22. Saturday evening thunderstorms broke up a streak of hot and humid weather, washing most pollutants off the landscape into the water and downstream prior to sampling on Monday morning. Coincidentally, Friends’ Monday sampling this summer has not yet fallen on mornings after rain and, therefore, has not yet captured data that would show pollutant loading from stormwater runoff.
Due to a week of very high air temperatures, Mad River water temperatures have increased dramatically since the last sampling on July 8, ranging from 64F in the headwaters (up from 55F) to 71F (up from 67F) along the Moretown Main Stem, with a high of 77F at Blueberry Lake (up from 73F). Despite the fact that water temperatures were higher, the Mad River Valley took to their favorite swim holes in droves this past week to get a break from the ever present heat.
“Thankfully, our river waters have not suffered from toxic algae blooms in the same way as lake water in several other Vermont locales and remain swimmable. While this may be fortunate for us, the pollutants we send to Lake Champlain (when it rains) do contribute to its sometimes poor water quality in other Vermonters’ favorite swim holes,” explained Corrie Miller, Friends of the Mad River executive director.
At the time of sampling on Monday morning, the river's discharge (volume per second) was 87.4 cubic feet per second (cfs) at the U.S. Geological Service flow gage in Moretown (only 6 cfs higher than the lowest yet this summer), having dropped from a high of 149 cfs overnight Saturday after the thunderstorms passed through. The flow condition of the Mad River at the time of sampling Monday morning was low and steady (LS), but began to rise just after sampling due to soaking rain later Monday morning. The mean flow for this date over the last 90 years is 100 cfs; the water was only slightly lower than usual at this time of year.
Rains can cause E. coli levels to fluctuate, even on a daily basis, as water carrying pathogens moves down the watershed. Monday’s rain most definitely washed pollutants into the water. Friends’ E. coli sampling results are only a snapshot in time intended to give people a sense of the conditions that lead to high pathogen levels in the water so they can be informed.
“You are your best protector -- use common sense and don't swim for several days after a rain. It is estimated that at the level of 235 colonies of E.coli per 100 mL water, approximately eight out of every 1,000 swimmers are likely to contract a waterborne illness related to fecal contamination,” Miller said.
As part of the Mad River Watch program, community volunteers collect samples of water on six occasions throughout the summer from about three dozen rivers and tributary sites. Then, Friends of the Mad River’s lab and Vermont’s Agriculture and Environmental Laboratory (VAEL) analyze the samples’ bacteria and nutrient levels. Friends of the Mad River posts E. coli data in The Valley Reporter, on its Facebook and web sites, and on signs at 10 popular swim holes across The Valley so that people have information to make their own recreational health decisions. In addition to E. coli data, Friends of the Mad River posts total phosphorus and nitrogen data on its website at summer’s end when received back from the state lab. Over the decades, Friends of the Mad River has used Mad River Watch data to guide many successful clean-up efforts.
This week’s volunteers include: Charlie Baldwin, Sally Boudreau, Suze Edwards, Annie and Jula Fender, Rick Hungerford, Susanne and George Schaefer, Michael Ware, and Julie and Ingrid Westervelt.
For more information about E. coli and the Mad River Watch program visit www.FriendsoftheMadRiver.org. Throughout the summer, Mad River Watch results will be available in The Valley Reporter, on Facebook (“Friends of the Mad River”), and on sign posts at swim holes across The Valley.