Colorado’s rainy May has ramped up the long-running rescue of four endangered fish species that face multiplying nonnative predators.
Heavy rain put enough surplus water in western Colorado reservoirs that state and federal operators last week were able to conduct coordinated releases, sending a surge of 4.5 billion gallons a day into the Colorado River — simulating natural spring high flows.
This surge revives the river habitat that humpback chubs, razorback suckers, bonytails and pikeminnows need to survive.
“We can create natural runoff conditions, and these native fish respond well to that,” federal hydrologist Jana Mohrman of the U.S. Fish and Wildlife Service said.
“They’re beginning to spawn in their natural habitat again,” Mohrman said.
Reservoir operators releasing stored water for fish breaks a pattern of drought and low flows along the highly controlled upper Colorado River.
The regulated flows have favored non native fish, such as the northern pike, which have increased exponentially since the drought of 2002. They attack and generally outcompete Colorado’s native fish.
It looked as if this summer would be especially difficult. On May 1, federal forecasts projected exceptionally low flows due to low snowpack in the mountains.
But May rain reversed that, filling reservoirs on both sides of the Continental Divide.
Front Range cities diverted less water, and the Dillon, Granby, Green Mountain, Ruedi, Williams Fork and Wolford Mountain reservoirs are able to release surplus water.
Colorado River flows have spiked. Federal data show projected inflows where the river reaches Lake Powell in Utah increasing during May to 70 percent of normal, up from 35 percent.
“It’s amazing to go from 35 percent to 70 percent of normal,” Colorado River District manager Eric Kuhn said. “We went from a severely dry year to a moderately dry year.”
The rush of water from coordinated releases sends signals to fish that trigger spawning.
Each year since 1995, Fish and Wildlife officials have tried to simulate spring high flows to help save the federally protected native chubs, razorback suckers, bonytails and pikeminnows of the upper Colorado River Basin.
These efforts traditionally depended on snowpack. But water agencies, including Denver Water and Northern Water, increasingly are trying to harness rain to achieve the same goals.
Bruce Finley: 303-954-1700, bfinley@denverpost.com or
