Fisheries experts urge caution as temperatures rise

Christine Peterson, Casper Star-Tribune photo An angler casts for carp at Flaming Gorge Reservoir. Fisheries experts are advising anglers that warm summer weather and low river flows will put a strain on trout, so when temperatures get high, it might be time to fish for other species, such as carp.

CASPER — The numbers are staggering. 

The Encampment River in southeast Wyoming usually runs about 900 cubic feet per second at the end of June. This year it was at 125 cfs and dropping. 

Only 43 percent of the normal amount of water is running from the mountains into Fontenelle Reservoir in southwest Wyoming. 

The Green River is usually between 2,000 and 10,000 cfs this time of year. Right now it’s around 700 cfs. The Green River as it flows through its namesake town had been hitting up to 75 degrees during the day and dropping back down into the high 60s at night in mid-June.

“None of those temperatures make trout happy, but they can survive those. But once you start getting 80 and above, they can start getting disoriented,” said Robb Keith, Wyoming Game and Fish Department’s Green River fisheries supervisor. “Their physiology isn’t set up to handle that warm water.” 

If water temperatures are sustained in the 80s, trout will die. 

The warm water temperatures and low water levels are partly due to a historically hot June, but also low snowpack in the winter and little moisture in the past few months. 

More than 2.5 inches of precipitation usually falls on Rock Springs between April 1 and the end of June, for example. This year, residents have seen just over half an inch, said Chris Jones, a meteorologist with the National Weather Service in Riverton. 

The rest of the summer forecast into fall isn’t any better. 

“And unfortunately with the hot, dry conditions we started with, those conditions feed themselves,” Jones said. “The soils are dry, and without moisture the temperatures get warmer and that feeds it further and it can be something that becomes more difficult to overcome.” 

What does this mean for anglers still hoping to make the most of this abnormally hot summer? Be aware of river and lake temperatures, said fisheries experts, and in many cases, get creative. 

Most fisheries biologists recommend when river temperatures reach the high 60s or 70s you stop catch and release fishing. While those temperatures won’t kill trout outright, trout have a much harder time if they’re expending energy being pulled from the water, fighting a line, hoisted out for a photo and placed back in. 

“The fish they’re catching will have to metabolize that lactic acid they built up fighting, and that gets hard on them when oxygen levels drop,” Keith said. 

Anglers itching to get on the river can go early in the morning when temperatures are cooler.

Lakes and reservoirs are sometimes no different. Fish like lake trout and kokanee struggle to survive being pulled from 45 degree water near the bottom of reservoirs up through 70 or 80-degree water near the surface, he said. 

“People release them and you end up with floating kokanee,” he added. “If you catch your three-fish limit, keep them and quit fishing or fish for lake trout pups or rainbow trout.”

Similarly, if a river allows you to keep fish, catch your limit, put them in the cooler and head out, said Nick Walrath, Green River Project coordinator for Trout Unlimited. 

And remember to bring along a thermometer so you can check the temperature of the water if there’s any question. 

Just because the rivers are warm and lakes dangerous for salmonid fishing doesn’t mean you have to stay home. 

High mountain streams are likely still cool enough to catch and release, Keith said. You can also think about fishing high mountain streams for fish like brook trout and keep your limit for a fish dinner or two. 

Or think about targeting other species, Walrath said. Head to places like Flaming Gorge and cast in the flats for carp. They’re big and fight hard. 

While Keith worries about additional pressure on trout from anglers, the fishing is about to get harder. Moss has begun to form and float down the Green River below Fontenelle Reservoir making angling tricky. Trout are also more likely to hunker down in deep, cooler pools of water with suppressed appetites. 

Low runoff also means less ash and soil dumping into the upper North Platte River after last summer’s historic Mullen Fire, said Bobby Compton, Game and Fish’s Laramie region fisheries supervisor. Massive ash runoff and erosion into rivers can also kill large numbers of fish.

Lastly, prolonged drought and increasingly warm temperatures reinforce the need to work on stream restoration and connectivity, Walrath said. The healthier the stream — with fewer culverts and less erosion — the better species like trout will be able to survive in a changing climate.

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