The Iowa Department of Natural Resources investigated a fish kill in Backbone State Park on Saturday after anglers reported dead fish in two trout streams.

Staff from DNR parks, environmental services and fisheries found dead trout and nongame fish in Richmond Springs and Fenchel Creek, the DNR reported. They also found some live fish, which means this is considered a partial fish kill. Investigators have not yet identified a pollutant source.

“Heavy rains Friday night may have washed contaminants into the streams,” the DNR said in a news release. “Prompt reporting by trout anglers meant investigators could quickly look for a pollutant source.”

The news release does not say how many dead fish were found or what substance likely killed the fish.

Richmond Springs is a “very popular fishery stocked twice per week” from April to October with “catchable brook and rainbow trout,” according to the DNR’s Where to Fish website. “The stream also contains a moderate-density population of wild brown trout.”

Backbone State Park, Iowa’s oldest state park, has had persistent problems with high bacteria levels causing swimming advisories at the beach there. State officials don’t know whether the feces found at high levels in Backbone Lake are from livestock, humans, or wild animals such as geese.

The state park near Strawberry Point is in a part of the state with karst topography, which is porous and allows pollutants to quickly absorb to underground water sources.

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