Warmer than normal water temperature endangering trout across Colorado
July 15, 2018
Colorado's fish are in hot water. Low river flows and high water temperatures are endangering trout in rivers and streams across the state, and wildlife officials are urging anglers to fish early in the day and take their lines out when water warms in the afternoon.
"We're experiencing some extreme high water temperatures in some of our rivers and streams, high enough to stress out trout," said CPW aquatic biologist Jon Ewert, who oversees aquatic life in Grand and Summit counties.
Ewert said trout thrive at water temperatures around 50 degrees, become lethargic in the 60s and very stressed in the 70s. Trout mortality is likely at 74 degrees and above.
The worry about water temperature is verified by data from the water monitoring gauge at the Pumphouse recreation site near Kremmling, a popular place for wade and float fishing. At one point this season, water temperature there reached 70 degrees and have since been holding steady between 60 and 70.
"We're in the worst shape when it comes to conditions," said Lori Martin, CPW's senior aquatic biologist for Northwest Colorado. "The snowpack melted early, and it's constantly hot and dry."
Martin referred to the snowmelt that peaked in mid-May in Summit, a month earlier than usual, causing water flows to bottom out much earlier in the season.
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Historical data from the Pumphouse gauge showed the typical water flow at this point in July is about 1,200 to 1,400 cubic feet per second. But this year, water levels peaked in mid-June and have been hovering at about 850 cfs for more than a week.
Water levels are important when it comes to temperature, as higher levels mean water warms more slowly, while the opposite is true for lower levels. With early melt-off, the hottest part of the summer is coinciding with the lowest water levels.
"That's something that's more typical in August, but not June and mid-July," Martin said.
The situation got so bad near Steamboat Springs that CPW initiated a voluntary fishing closure for a stretch of the Yampa River, asking anglers to avoid fishing that area to keep the trout stock healthy.
The same voluntary closure might occur in Summit, and local fishing businesses are worried.
"Our guides have been going out as early in the morning as possible to get full-day trips in," said Chris Refakis, of Cutthroat Anglers in Silverthorne. "Once the water temperature reaches 65 at around noon or after, we shut down all fishing."
The time cutoff is critical. Ewert said anglers should not be fishing after 1 p.m., as that is the hottest part of the day and the time fish are most stressed.
Jack Bombardier, speaking for the Gypsum-based fishing outfitting company Confluence Casting, said he, too, has been forced to spend the second half of day trips on more scenic tours, when the water gets warm and his customers need something to do.
"At one point, it was like wading through bath water," he said.
Bombardier said conditions became bad enough in the spring, when water flows were half what they usually are, that he and other members of the Upper Colorado River Wild and Scenic water stakeholders group requested a water release from Denver Water and other water reservoir owners to increase river water flows.
However, that was considered an emergency measure, and new requests for water releases will be difficult to grant.
"It's a little frustrating that these reservoirs are full, but they're not letting any of it out," said Bombardier. "But the primary function of those reservoirs is for human consumption to mitigate low summer flows and not for fish."
As with anything water-related this summer, hope comes in the form of rain. Monsoon season is expected to be wetter than average, and the cloud coverage is expected to help cool streams enough to keep trout happy. Ewert said the water temperature situation isn't dire yet, but if rains don't come soon, the state may likely consider voluntary fishing closures in Summit County.