A water sample taken just south of Brandon, shows E. coli levels after the record rain were almost 200 times higher than allowable limits.
Friends of the Big Sioux River took the water sample on August 9, just two days after the area received record-breaking rainfall. Travis Entenman, managing director of Friends of the Big Sioux River, said he wasn't surprised.
"It's probably twofold; cattle in the water body, and excess manure on fields that the crops, or the soil, were unable to bring in before the rain hits," Entenman said.
The water samples came from a section of Slit Rock Creek — a section designated by the state as water that needs to be clean enough for fishing, kayaking, and other activities that don't involve getting into or drinking the water.
For E. coli, that means fewer than 126 E. coli colonies per 100 milliliters of water — the sample had 24,200 colonies.
"Very rarely do we get over 1,000 and up to 24,000, but it does happen probably once or twice a year," Entenman said.
He said, regardless of rainfall, 78% of South Dakota streams and rivers have contaminant levels that are above what the state designates as reasonable.