Recently, several hundred fish have been found dead in the El Dorado East Park Pond.
City of El Dorado Public Utilities Director Kurt Bookout says overcrowding of geese and ducks were assumed to be the source of the problem.
"It just overwhelms the small pond that's only a half acre in size gets too many animals in there, too much organic material," Bookout said.
He continued by saying too much organic material can lead to algae blooms, which can cause dissolved oxygen problems, in turn killing the fish.
But a test of the water revealed normal oxygen levels, something Bookout says might be misleading.
"We found that the oxygen levels can be diurnal," Bookout said. "We can have adequate oxygen during the day and inadequate during the night."
The city is still testing the water to see if the oxygen levels are low at night.
In the meantime, a line from El Dorado lake is bringing fresh water in, and some of the geese have been relocated.
The fish that died were mostly small blue gills. The city says this is not the first time this problem has occurred at this pond, but that it is probably the worst it has been.