Study: Hydropower Decimates Aquatic Insects on the Colorado River

May 5, 2016

Several species of aquatic insects are mysteriously missing from the Colorado River in the Grand Canyon. Scientists now know that’s because dam managers rapidly change the river’s level to meet electricity demand.

Citizen scientists collect insects with a light trap in the Grand Canyon.
Credit Dave Heramimtschuk-USGS/Freshwater Illustrated


The practice is called “hydropeaking” and it causes wide fluctuations in the Colorado River’s flow.

Scientists connected hydropeaking to the strange absence of certain aquatic insects below Glen Canyon and Hoover Dams.  

Ted Kennedy of the U.S. Geological Survey in Flagstaff led the study. “It turns out many aquatic insects have egg laying behaviors that are dependent on river edge habitat, where they’re affixing their eggs to rocks and vegetation along the river shoreline,” he says. “And they don’t realize that in 12 hours the water’s going to drop out and leave those eggs high and dry.”

Just an hour of desiccation kills the eggs. That’s a big reason why mayflies, stoneflies and caddisflies can’t be found in the Grand Canyon. These insects are indicators of ecological health and vital food sources for fish and wildlife.   

Kennedy says one solution is to provide low, steady river flows on weekends, when electricity demands aren’t as large. These so-called “bug flows” could create ideal egg laying conditions.

The U.S. Bureau of Reclamation is accepting public comments on proposed operations of Glen Canyon Dam until Monday, May 9. For more information, click here.  

The study appeared this week in BioScience. It relied on more than 2,500 insect samples collected by citizen scientists on river rafting trips.