Survey confirms Snake River fish kill | AspenTimes.com

Survey confirms Snake River fish kill

Bob Berwyn
Summit County correspondent
Aspen, CO Colorado

Biologists, working with Colorado Division of Wildlife, along with volunteers, walk the Snake River near Keystone Tuesday, electro-shocking and netting fish while doing studies and testing as a follow-up to recent fish kills on a stretch of the Snake. (Mark Fox/Summit Daily)

SUMMIT COUNTY – Standing hip-deep in the swift water of the Snake River near Keystone, it’s hard to see how a fish wouldn’t like it here. At first glance, it’s a pristine mountain stream, lined with willows and glacier-polished boulders.

But the water has a slight tinge to it, still milky green from a pair of recent storm events that may have sent a surge of toxic heavy metals, as well as a killer load of silt rushing down the stream.

“It doesn’t look quite right,” says local angling guide Dale Fields, pointing out where a layer of fine brown mud has settled on the gravelly banks of the river. Fields, who has been fishing local waters for more than 20 years, thinks the rainstorms in early August probably unleashed a heavy load of sediment that choked most of the fish in this section of the Snake River.

One of the thunderstorms, centered above the Peru Creek tributary, may have also have flushed higher-than-normal loads of toxic heavy metals downstream, also contributing to a high mortality rate among the stocked rainbow trout in the vicinity of Keystone.

Hundreds of fish may died following the pair of storms, Fields estimates, and Tuesday’s effort to find and count trout in a 500-foot section of the stream just downstream from River Run was aimed at determining whether any fish survived.

After firing up a portable generator on the shoreline, Colorado Division of Wildlife aquatic biologist Jon Ewert hands out long-handled electric probes and nets and gives the team some basic safety instructions. A fall into the river near the probes isn’t advisable, he says, adding that he will closely eye the wading volunteers, ready to pull the plug at a moment’s notice.

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The idea is to scour every inch of river bottom and every undercut embankment and shady hole where a flashy rainbow or a speckled brook trout might be hiding. If a probe passes within a few feet of a fish, it stuns them, and they float to the surface where they can be netted, then measured and weighed.

It’s slow going, walking upstream on slippery rocks and trying to make sure that the wands pass over every possible inch of good habitat, all while staying balanced in the sometimes fierce current.

Several weeks ago, a similar survey in the same stretch of river yielded about 40 to 50 fish, Ewert says. But Tuesday’s effort only turns up two small brook trout that might be re-colonizing the area, perhaps washed downstream by the same floods that apparently killed nearly every one of the stocked rainbows.

Fields and Ewert agree that the Aug. 3 and Aug. 9 storms likely killed nearly every fish in the river from Keystone downstream, but they aren’t on the same page when it comes to the cause.

At least during the first storm, Ewert thinks the toxic metals known to be present in Peru Creek likely played a significant role in the mortality. But Fields says the fish died too fast – within a few hours of the event – to pin the blame on the discharge from abandoned mines high in the drainage. Based on visual observations of the river turning brown as chocolate milk, a heavy load of silt is the more likely cause, he says.

“The fish started dying within hours. That’s not a toxic reaction,” Fields says. When it comes to sediment, trout are highly susceptible, even loads as small as three to four parts per million can suffocate fish, explains Fields, who is also part of technical task force working on Snake River issues.

On the other hand, Ewert says that, if the fish were already stressed from ongoing exposure to metals, a sudden spike in the concentrations could have been enough to kill.

But at this point, it’s almost impossible to know for sure, since none of the dead fish were recovered and sent to a lab for analysis, where a close examination could reveal concentrations of metals in fish tissue. Nor did local water quality officials take water samples during the runoff events, so there’s no way to know for sure whether there was a sudden surge in the concentrations of metals.

Whatever the exact cause, the paltry tally from Tuesday’s fish count confirms the bad news. It appears that the rainbow trout population has been completely wiped out, though Keystone plans to restock the river at the end of August, in time of the Labor Day weekend.

“It definitely indicates there was … a shock to the river,” Fields says, cautioning against waving the red flag of acid mine drainage without having any definitive evidence.

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