State wildlife officials are investigating a large fish kill in southern Minnesota, along a designated trout stream on the South Branch Whitewater River just upstream from a state fish hatchery near the town of Altura.

The Department of Natural Resources (DNR) said late Friday that fisheries staff found thousands of dead fish over about 3 miles of the stream after being alerted Thursday morning by a local fisherman.

The area received heavy rain on Monday night and Tuesday morning that might have flushed contaminants into the stream.

DNR spokesman Harland Hiemstra declined to speculate on the cause, but said the Minnesota Pollution Control Agency and the state Department of Agriculture have joined the investigation.

The dead fish included brown trout, rainbow trout, suckers, chubs and minnows ranging in size from about 2 to 18 inches long.

Ron Benjamin, a fisheries supervisor in Lanesboro, said the fact that everything died indicates some kind of spill or pollutant that contaminated the full stretch of water.

By Friday, the stream was back to normal after natural stream flow apparently cleansed the water, officials said.

“We see about 2 to 5 of these a year,” Benjamin said. “For that little piece of stream, it’s a big one. But it’s not catastrophic.”

 

Staff writer Josephine Marcotty contributed to this report.