The Wyoming Game and Fish Department has raised the alarm about soaring water temperatures, telling anglers to stop fishing after noon on parts of the Green River so they don't unintentionally kill fish.
The moratorium on afternoon catch-and-release fishing remains purely voluntary for now, Game and Fish stated.
And across Wyoming, fishing guides have broken out thermometers and started monitoring water temperatures.
A water temperature of 70 degrees is widely considered the red line, particularly for trout, avid angler and fishing guide Bradey Hall of Casper told Cowboy State Daily.
"Most of the guides, when we're out fishing and the water starts hitting 70 degrees, we're done," he said.
"Trout are cold-water fish. When the water is warm and they fight so hard, they just fight themselves to death," Hall added.
Lay Off Green River Section
Game and Fish is asking anglers to quit catch-and-release fishing from noon until sunrise on the Green River between Slate Creek Campground and Flaming Gorge.
"Unseasonably warm temperatures and low flows" are causing the water temperature on that stretch of river to exceed 70 degrees every afternoon and evening, according to Game and Fish.
"Signs explaining the voluntary closure will be posted at major public access points," according to the department.
That section of the Green River supports one of Wyoming's most prized trout fisheries, regional fisheries biologist John Walrath said.
"As water temperatures rise during the summer, trout experience greater stress after being caught and released. By voluntarily shifting fishing to the cooler morning hours, anglers can make a meaningful contribution toward protecting this fishery," he wrote.
Game and Fish recommends that anglers carry a pocket thermometer and consider catching only fish they intend to keep once the water temperature hits 65 degrees.
"Once water temperatures reach 70 degrees, anglers should discontinue catch-and-release fishing altogether," according to Game and Fish.
Water temperatures of 68 to 70 degrees can cause trout to suffer a fatal buildup of lactic acid after being hooked and fighting anglers' attempts to land them.
Warm water contains lower levels of dissolved oxygen. Prolonged exposure to water temperatures over 75 degrees can kill trout, as can even brief exposure to temperatures of 80 degrees and above.
'Pretty Hot, Pretty Fast'
On Wyoming's famed North Platte River, anglers and guides take it as practically a given that there will be days during the summer when the water gets too hot for safe catch-and-release trout fishing, Hall said.
But that's usually not until August, and this summer there were days in July that hit that water temperature threshold, he said.
"It seems like they (water temperatures) are getting pretty hot, pretty fast this summer," he said.
The "Miracle Mile" stretch of the North Platte is actually about 8 miles long.
The upper three miles were recently closed to watercraft.
Hall said that, by his estimation, that created increased competition for wade-only fishing on the upper stretch.
So, more wading anglers have migrated to the lower section, increasing pressure there.
Even so, as long as everybody is mindful of the water temperature, "the fishing has been really good" and should stay that way.
'No Bueno'
Trent Tatum, co-owner of the North Platte Lodge and The Reef Fly Shop Cottages and RV in Alcova, told Cowboy State Daily that water temperatures have so far stayed in the high 50s to low 60s on the sections of river where his company guides trout anglers.
"We're pretty diligent. We have guides taking water temperatures every day," he said. "If you get into water that's 68 degrees or higher, that's no bueno.
"My concern will be in August. If they decide to lower our water flows below the dams on the North Platte, the water temperature could become an issue."
Mark Heinz can be reached at mark@cowboystatedaily.com.
