Dead fish

A dead brown trout lays on the bank of the Madison River. Montana Fish, Wildlife & Parks fisheries biologists have collected samples of dead and dying fish for testing. 

Quincey Johnson, Upper Missouri Waterkeeper

Testing of dead whitefish and trout on the Madison River below Ennis Dam has shown the mortality stemmed from irritated gills, but a causative agent was not determined, according to Montana Fish, Wildlife & Parks.

In May, FWP counted 800 dead whitefish and 20 dead trout on the river and collected several for testing. The fish kill extended over a 10-mile stretch of the river from Ennis Dam to the Warm Springs Boat Launch.

FWP staff have since received reports of brown trout with saprolegnia infections. Saprolegnia is a white, cotton-like fungus that can kill fish in certain conditions. Subsequent sampling efforts confirmed the presence of saprolegnia in several brown trout captured in Bear Trap Canyon.

The presence of the fungus factored into the decision by FWP to prohibit fishing each day between 2 p.m. and midnight from the dam at Ennis Lake downstream to the Madison River’s confluence with the Jefferson River at Missouri Headwaters State Park. The restrictions run through Aug. 15.

Water temperatures in the lower Madison have exceeded 75 degrees each day since June 21, meeting the criteria for hoot-owl restrictions.

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