Click the link to read the Runoff on the Aspen Journalism website (Heather Sackett):
August 2, 2024
‘We’re reengineering the river in even crazier ways’
In an effort to prevent smallmouth bass — an invasive, voracious predator that feasts on native fish, including the threatened humpback chub — from establishing populations below Glen Canyon Dam, the U.S. Bureau of Reclamation in early July began releasing colder water from Lake Powell via the river outlet works (which are 100 feet lower in a cooler part of the water column) in addition to the hydropower penstocks. Known as the “Cool Mix Alternative,” Reclamation chose this option with the goal of keeping water temperatures below the dam under 15.5 degrees Celsius (60 degrees Fahrenheit), which is too cold for smallmouth bass to thrive.
But a report by a group of scientists at the Center for Colorado River Studies at Utah State University says that factors other than temperature should be taken into consideration when trying to manage the nonnative species. The Western Area Power Administration, which sells the hydropower generated by Glen Canyon Dam, funded the participation of two of the four scientists who authored the report.
The report says the nearest population center of humpback chub is 76 river miles downstream in Grand Canyon water that is too turbid for smallmouth bass to proliferate.
“We think the uncertainty in predictions about smallmouth bass establishment near the downstream humpback chub population centers and their impact on chub populations if smallmouth bass do become established is not adequately recognized,” the report reads.
The report urges water managers to not develop reservoir operation plans that are too prescriptive given the uncertainty about hydrology in the coming years.
“We think the various management actions being considered to control smallmouth bass recruitment are unlikely to be effective given the modest history of success of similar actions in the last two decades in the Colorado River ecosystem,” the report reads. “We recognize that our report differs from the dominant paradigm related to smallmouth bass in the Colorado River basin and that even suggesting this alternative paradigm will likely create disagreements among scientists and … stakeholders.”
Jack Schmidt, a Colorado River expert, professor and lead author on the report, said that it’s ironic that in order to preserve one of the last remaining native components of the river’s natural ecosystem (humpback chub), water managers are looking to increasingly unnatural actions on the already highly engineered river. Messing with nature only begets more messing.
“We’re making the river more unnatural, and we’re reengineering the river in even crazier ways to try to protect the remaining elements of the native ecosystem,” Schmidt said. “And although the intentions of that are incredibly well-meant, over the long run, that may not be possible. … At what point does making the river more unnatural just not make sense anymore?”
What is another way to ensure that releases out of Lake Powell’s hydropower penstocks are cold enough to prevent the establishment of smallmouth bass? Keep the reservoir more full. But with the effects of steady demand, drought and climate change, that’s easier said than done.
