Most kinds of E. coli are harmless to humans, but some can cause diarrhea, urinary tract infections and respiratory illness.
It's that potential that has some in KOTA Territory worried about bacteria in creeks and streams.
Sheridan mother of two Camielle Turley brings her kids to Kendrick Park "probably three times a week or more."
But Turley said hearing about high levels of E. coli in Goose Creek, the waterway that runs through the park, is giving her pause.
"I used to let my daughter just walk through the water," she said, "and I may not let her do that as much."
That's because the Sheridan Conservation District is finding levels of E. coli more than three times the level the state says is safe.
"It's one of those that is transported through runoff, whether it's through rural subdivisions, ranches, ranchettes, city storm drains," said Conservation District manager Carrie Rogaczewski.
Since 2001, Rogaczewski has measured E. coli at levels as high as 450 colony-forming units per hundred milliliters in Goose Creek, and up to 900 units in its tributaries.
The state standard is 126.
"It's enough to make you think that it is, in fact, over the standard and not just an anomaly for that year or that site," she said.
But just how harmful it is still isn't clear.
Rogaczewski said levels that high could indicate higher levels of other pathogens, but the agency has just started testing this year.
"What we expect to see will be similar, I think, to years past," Rogaczewski said.
Which, for Turley, means business as usual.
"I'll bring them just as much still," she said, "so it's not that big of a worry"
The city is working on several measures to cut back contamination, like riparian buffers and other ways to filter runoff before it gets to major waterways.