The good and bad effects of spring runoff

My recent perusal of www.waterdata.usga.gov showed most Montana rivers are still running two to three times normal flow. That's a lot of water to deal with while floating and fishing. Most streamflows are dropping, but anglers are urged to stay alert as river channels may have changed.

So, where did the fish go in the Flathead River to wait out the high and sustained water flows? According to Jim Vashro, Region 1 fisheries manager for the Montana Department of Fish, Wildlife and Parks, "Fish have evolved in this river system, and it certainly wasn't the first high water they've seen."

Vashro says trout sought quiet eddies and grouped behind big boulders, where they didn't have to fight a strong current.

"Most likely, the fish partitioned by size, the largest fish holding down the most secure spots," he said.

High water not only scoured the stream bed but also floated away streamside debris, including downfalls. While scouring cleans up the river bottom, Vashro says, we may see a weak year-class of fish, especially westslope cutthroats, due to loss of hiding places and increased predation.

"The rainbows may have done better than cutts because they spawned earlier," Vashro added. "High water carries sediments that are deposited in riparian zones as water levels drop. Down the road, these fresh soil nutrients enhance the growth of streamside vegetation, including black cottonwood. So although we may be looking at a short-term hit, we may see some long-term benefits."

According to Vashro, this year's Flathead River runoff had two effects on Flathead Lake.

"We may have gotten a good perch hatch this spring, but we're afraid the cold water stopped zooplankton development and the tiny perch may have starved," he said.

Lake whitefish typically feed on schools of perch in mid-July and provide one of the most popular fisheries in Flathead Lake.

"Sediments also deposit nutrients into Flathead Lake," Vashro said.

As Flathead Lake clears and warms, the nutrients will promote increased growth of vegetation, which may be good for some fish but also hastens eutrophication.