Bugs Benefit From Low Weekend Flows on Colorado River

May 9, 2019

Low, steady releases of water from Glen Canyon Dam are taking place this spring and summer as an experiment to increase aquatic insects on the Colorado River. KNAU’s Melissa Sevigny reports, these “bug flows” benefit the river’s ecology and might even help anglers catch more fish.

Credit Grand Canyon National Park / Erin Whittaker


Under normal dam operations, the Colorado River’s level fluctuates widely with hydropower demand. That can harm insect populations because their eggs dry out when the water drops. But the “bug flows” create the right conditions for egg laying. The experiments take place on weekends when hydropower demand isn’t as high.

"Bugs are the food base for the entire Colorado River," says Jeff Muehlbauer, an aquatic ecologist at the Grand Canyon Monitoring and Research Center. "If we can get more bugs, the idea is we'll be promoting conditions for the entire ecology of this place."

Muehlbauer says data collected during last’s year’s bug flow showed a 4-fold increase in caddisflies. Also, a survey by the Arizona Game and Fish Department found anglers at Lees Ferry caught 18 percent more fish during the experiment.

Biologist Dave Rogowski speculates that’s because the river is easier to fish. "Steady, lower flows make it more like a natural river, I guess," he says. "Most rivers do not fluctuate 2 to 3 feet in a day. When that happens it can affect the behavior of the fish."

River managers will continue the bug flows through August and hope to repeat them next year.