Biologists’ fears confirmed on the lower #ColoradoRiver — The Associated Press #COriver #aridification

The Colorado River from Navajo Bridge below Lee’s Ferry and Glen Canyon Dam. The proposed Marble Canyon Dam would have been just downstream from here. Jonathan P. Thompson photo.

Click the link to read the article on the Associated Press website (Brittany Petersen). Here’s an excerpt:

For National Park Service fisheries biologist Jeff Arnold, it was a moment he’d been dreading. Bare-legged in sandals, he was pulling in a net in a shallow backwater of the lower Colorado River last week, when he spotted three young fish that didn’t belong there. “Give me a call when you get this!” he messaged a colleague, snapping photos.

Minutes later, the park service confirmed their worst fear: smallmouth bass had in fact been found and were likely reproducing in the Colorado River below Glen Canyon Dam.

The confluence of the Colorado and Little Colorado rivers in the Grand Canyon, shown here in a September 2020 aerial photo from Ecoflight, represents an area where the humpback chub has rebounded in the last decade. That progress is now threatened by declining water levels in Lake Powell, which could lead to non-native smallmouth bass becoming established in the canyon. CREDIT: JANE PARGITER/ECOFLIGHT

They may be a beloved sport fish, but smallmouth bass feast on humpback chub, an ancient, threatened fish that’s native to the river, and that biologists like Arnold have been working hard to recover. The predators wreaked havoc in the upper river, but were held at bay in Lake Powell where Glen Canyon Dam has served as a barrier for years — until now. The reservoir’s recent sharp decline is enabling these introduced fish to get past the dam and closer to where the biggest groups of chub remain, farther downstream in the Grand Canyon.

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