Lake Herman Dirtiest in October, Still Safe

We volunteers in the Dakota Water Watch bacteria monitoring project took our last samples for 2010 on October 12. The biology lab at Dakota State University just sent back the draft results for the season.

Charlie Stoneback and I sampled five different sites on our Lake Herman through summer and fall. The highest E. coli ratings for the year came this month, in that warm October weather. Charlie got the highest bacteria reading, 210 colony-forming units per 100 mL, at the sample site right next to his house, at the mouth of the golf course creek. That was over twice as high as the reading he got at the same site in July.

The next highest October readings were at my two sites: 144 cfu/mL at the mouth of the stream on the south tip of the lake, 100 cfu/mL at the mouth of the stream that runs into the lake from the southwest, next to Camp Lakoida. I never got a reading over 100 in any of my other 2010 samples.

What do these numbers mean? Well, there's some E. coli in Lake Herman, and the little buggers apparently enjoyed the warm October weather that didn't really break until this weekend. But even Charlie's high number doesn't exceed the Environmental Protection Agency's single-sample maximum for immersion recreation of 235 cfu/mL (environmental scientists, check that number for me!).

In other words, swimming in Lake Herman is still relatively safe. And we're still filtering nutrients and keeping the water a little cleaner and the property values a little higher at Lake Madison.