Low Water Levels in Colorado River Boost Population of Invasive Fish

The Colorado River's low water levels are putting native fish in danger and threatens a possible increase in the population of invasive fish.

Swarm of Invasive Fish

Officials have warned that an invasive fish species may start to spread to more regions of the Colorado River. Concerns about smallmouth bass, an invasive species that has been established in Lake Powell, a reservoir on the Colorado River, escaping into other reaches of the river below the dam, were expressed in a report issued in February by the Bureau of Reclamation.

Some of Lake Powell's lowest water levels have ever been recorded are being caused by the Glen Canyon Dam. The dam has so far prevented the smallmouth bass from crossing it, but officials are worried that the very low water levels will allow the fish to do so. According to the report, high water levels make it difficult for fish to pass through.

Smallmouth Bass in Colorado River

Originally from eastern North America, the smallmouth bass is warm-water predatory fish.

The Colorado River ecosystem has been impacted by the invasive species for the past 20 years, according to the National Park Service. They severely harm the ecosystem by gorging on other native fish species.

Officials from the National Park Service discovered smallmouth bass juveniles in the water below the Glen Canyon Dam in July 2022.

The Colorado River reservoirs experienced a particularly dry July last year, and this year may be no different. The water levels in Lake Powell may continue to drop as the climate warms and dry conditions return.

A fish that is native to the Colorado River and is federally protected, the humpback chub, is of particular concern. They have been devoured by smallmouth bass as biologists work to save and recover the populations of the native species.

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Low Water Levels

Due to the severe drought that is gripping the US Southwest, the water levels in reservoirs along the Colorado River are rapidly dropping. The environment is perfect for the invasive species due to the warm, dry conditions.

The water levels in Lake Powell hit a record low in February of this year.

According to USA Today, the Colorado River reservoir, which is located in Arizona and Utah, reached a historically low elevation of 3,522.16 feet above sea level on February 14. Then, it kept dropping, until it reached 3,521.77 feet on February 18.

The water levels in Lake Powell are at their lowest point since the 1960s when the artificial lake was first filled.

The Bureau of Reclamation recently released a report outlining several plans to try and prevent the invasive species from procreating uncontrollably. One option is to try and prevent the fish from breeding by releasing cold water in the area. The bureau claims that efforts to eradicate the species would be made even more challenging if smallmouth bass began to spawn rapidly, Newsweek reports.

Smallmouth bass and green sunfish are found in the warmer lake waters near the surface, according to the National Park Service. The invasive predatory fish have a better chance of making it through the dam alive as the warmer water reaches the water intake of the dam. Due to this, native fish in the Grand Canyon and the rainbow trout fishery downstream of Glen Canyon Dam are now more in danger.

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