Rochester, MN (KROC AM News) - The Minnesota Department of Natural Resources says its investigators were not able to pinpoint the cause of a fish kill along a stretch of the Whitewater River near Rochester in July.

It was estimated that up to 10,000 fish, including brown and rainbow trout, died following a period of heavy rain on July 28th.

DNR officials says water samples showed there were no toxic levels of ammonia, pesticides or metals, and no insecticides were detected. Only extremely low levels of fungicides were found in the samples. Instead of a single cause, investigators can only speculate that the fish kill was the result of a combination of biological, chemical and environmental conditions related to the thunderstorm that delivered up to 2.5 inches of rain in the Whitewater watershed over several hours.

Officials also noted the investigation was hampered because two days passed between the heavy rainfall and the discovery of the fish kill.

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