Watching Montana’s Clark Fork River Come Back to Life


The Clark Fork, flowing through Missoula, Montana, is no longer the same river that it was when I lived near its banks during graduate school. Back then paddlers, swimmers, and fishermen had to contend with long green plumes of “rock snot” that blanketed the river bottom and made for difficult, slippery wading in river sandals.

Today one instead finds ever shifting gravel bars composed of clean, multi-colored rocks. It’s as if the Clark Fork River recently received a scrub.

In fact, beginning four years ago today, it did.

For 100 years, Milltown Dam sat at the confluence of the Clark Fork and the Blackfoot rivers a few miles upstream from Missoula. Built in 1908, the dam blocked sediment from moving downstream, warmed the water, and modulated river flows to such an extent that all that remained in the riverbed were large, stationary boulders.

This created the perfect conditions to grow Didymo (didymosphenia geminate), an algae also known by the disparaging name “rock snot.” And did it ever grow! Its slimy tendrils flapped lazily in the current, catching on paddles, swimsuits, and anglers’ flies, changing the color of the Clark Fork to a murky green.

But this changed after Milltown Dam was removed. Much of the sediment that collected behind the dam had washed downstream from mine tailings upriver, and was laden with heavy metals.

These pollutants contaminated the aquifer of a nearby town, killed fish, and earned the entire length of the Clark Fork River a “Superfund” designation by the Environmental Protection Agency (EPA). Toxic sediment removal began in 2006, and the dam was breached on March 28, 2008, after years of citizen involvement and tireless advocacy by local conservation groups like the Clark Fork Coalition and Montana Trout Unlimited.

Now, four years later, and after a particularly high spring runoff in 2011, the riverbed in this section of the Clark Fork River has been utterly transformed. What once was an algae farm is now a cold, clear, sediment-transporting, mountain-moving machine again!

Brightly colored rocks and gently curving gravel bars move and change with the seasons, providing spawning habitat for native Bull trout and Westslope cutthroat trout, as well as denying rock snot a foothold.

It’s great to see the gravel bars beneath Clark Fork River come alive again. Welcome back.