Periods of dry followed by rain lead to high E. coli levels
By: Corrie (friendv3) 2014.07.15

Sampling results from the third round of Friends of the Mad River’s 2014 Mad River Watch (MRW) volunteer water quality program show many swimhole sites with unfavorable swimming conditions yesterday. Fifteen of the 36 sites tested above Vermont’s Department of Health’s water quality standard in recreational waters (235 bacteria colonies per 100 ml of water), including many popular swimming holes. Of these 15 sites, 11 were main-stem Mad River sites and 4 were from tributary sites (Folsom Brook, High Bridge Brook, Shepard Brook, and Welder Brook). These high E. coli levels are to be expected given the days of dry weather leading up to rain on Sunday evening. As the rain washed pollutants through the watershed, E.coli levels in streams and rivers went up. The swimming might be more exciting in high water, but think twice before swimming after a storm!

E. coli is a type of coliform bacteria and is used as an indicator of pollution from human or animal waste and the potential presence of disease causing organisms. It is estimated that at the level of 235 colonies E.coli per 100 mL water, approximately 8 out of every 1,000 swimmers are likely to contract a water borne illness related to fecal contamination.

The flow condition of the Mad River at the time of sampling Monday morning was low and rising (LR), measuring approximately 96 cubic feet per second (cfs) at the USGS flow gage in Moretown, up from about 55 cfs mid-day on Sunday, after three days of relatively low water conditions. The median flow for this date is 107 cfs. Water levels rise and fall with rain, and you can expect E. coli levels to do the same! As runoff from the landscape washes into streams, E. coli levels can rise.

Many thanks to this week’s Mad River Watch volunteers: Michael Ware, Fran & Gary Plewak, Susy Deane, Sally Boudreau, Carol Chamberlin and Jody Chamberlin. Also, a big thanks to Cyndee Button, our volunteer Lab Coordinator, to Sally Boudreau for posting MRW data at swimholes, and to Stan Button who drove water samples to the Burlington lab for phosphorus and turbidity analysis!  

For more information about E. coli and the Mad River Watch program click here.

To view our most recent complete data report click here.

Friends is a membership organization, and depends on the generous contributions of members to continue the Mad River Watch and other programs; learn how to become a member and donate securely online.