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Fish Kill North Of Hinsdale Under Investigation

A widespread fish kill on Rock Creek and the Milk River north of Hinsdale is being investigated by Fish, Wildlife & Parks fisheries biologists.

A landowner reported the incident on July 13. Upon investigation, biologists observed dead fish downstream of the confluence of the Milk River and Rock Creek. Further searching found dead fish 9.5 miles from the mouth of Rock Creek up to the Rock Creek Dam, although the full upstream extent was not determined. No dead fish were observed in the Milk River upstream of the confluence with Rock Creek.

β€œWhatever killed these fish was highly toxic as it killed carp, bullheads, catfish and a host of warm water fish species that tolerate poor water quality,” said regional fish manager Steve Dalbey.

Species observed included walleye, northern pike, carp, catfish, goldeye, bullhead, shorthead redhorse, river carpsucker, white sucker, freshwater drum and buffalo.

Although the source of the fish kill was not determined, the timing and rate of decomposition of the fish suggest it may have occurred between July 9 and 11. The incident may be related to heavy rain that occurred on July 8 and 9, FWP speculated. According to the National Weather Service, a half-inch of rain fell the evening of July 8 and another quarter to an inch of rain fell the evening of July 9.

Live fish were collected in the area at the time of the investigation. No abnormalities were observed.

β€œAll of this points to a toxicant that may have entered Rock Creek above the Rock Creek dam during the rain events of July 8 and 9 and moved through the river,” Dalbey said. β€œIt’s difficult to pinpoint where this occurred unless more fish are found in and around the affected reach of river.”

FWP will follow up with fish collection from the affected area to look at possible contaminants in the fish tissue. Currently there are no fish consumption advisories.

If members of the public have any information on what may have led to this fish kill or have other questions or concerns, call the Glasgow FWP office at 406-228-3700.

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