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Federal officials complete slough work on Colorado River

An aerial view of construction work underway on April 3, 2025 at the -12 Mile Slough in Glen Canyon, which has become a breeding ground for nonnative fish.
Glen Canyon National Recreation Area
An aerial view of construction work underway on April 3, 2025, at the -12 Mile Slough in Glen Canyon, which has become a breeding ground for nonnative fish.

Federal agencies have finished digging out a side channel below Glen Canyon Dam that's been a breeding ground for nonnative fish.

The -12 mile slough is a shallow, mostly disconnected part of the Colorado River in Glen Canyon National Recreation Area. Since March, officials with the U.S. Bureau of Reclamation and National Park Service have worked to reconnect it to the main channel to bring in colder, faster water. That should discourage nonnative species from breeding there.

Smallmouth bass is a particular concern. It’s a predatory fish that poses a threat to native, endangered species in the river.

Federal officials also have plans to tweak releases from Glen Canyon Dam and introduce colder water to discourage nonnative fish.

But, a different program to release springtime artificial floods that help rebuild eroding sandbars in the Grand Canyon was cancelled this year, with officials citing the slough construction work as the reason.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.