The Bernice State Park swimming area at Grand Lake remains closed after another test revealed elevated levels of E. Coli.
Officials say lab test have revealed that geese and possibly other birds are the source the bacteria.
"When this swim area was initially closed in early June, the primary goal was to determine the source," said Justin Alberty, Grand River Dam Authority Communications Director. "These results show this to be a naturally occurring event and not anything man-made."
The beach will remained closed until the levels return to a safe range.
Officials say the Bernice shoreline is a favorite nesting area for a large population of geese. Recent heavy rains in the area likely led to geese waste being washed into the water, leading to the elevated bacteria levels.