ST. GEORGE — The Bureau of Reclamation is asking for public input on its draft environmental assessment designed to stop a predatory, invasive fish species from spawning below the Glen Canyon Dam.

As Lake Powell’s water levels continue to drop to historically low levels, water is being released through the Glen Canyon Dam at “record-high” temperatures, a news release issued by the Bureau states.

Although the invasive fish have previously been sighted downstream of the dam, the river’s warmer temperatures are “now conducive for smallmouth bass reproduction and establishment,” according to the draft environmental assessment.

While the smallmouth bass is a popular sport fish, the species “wreaked havoc” on the upper Colorado River, The Associated Press reported. However, until recently, they were “held at bay” by the Glen Canyon Dam.

Smallmouth bass pose a threat to native fish, such as the federally protected humpback chub, which is only found in the Colorado River Basin and is most abundant at the junction of the Colorado and Little Colorado rivers, according to the National Park Service.

While three chub species previously inhabited the Grand Canyon, only the humpback chub remains, with a 2009 population estimate of 6,000-10,000, the park service states.

If smallmouth bass or other predatory fish are established below the dam, there is a risk of “potentially unraveling years of restoration work and upending the Grand Canyon aquatic ecosystem — the only stretch of the river still dominated by native species,” the AP wrote.

Additionally, an established population could be expensive and difficult to remove, the assessment reads. Attempts to mechanically remove smallmouth bass from the Upper Colorado River Basin over the last 20 years “have had limited success.”

To mitigate the threat, the Bureau of Reclamation is seeking public input on the draft Glen Canyon Dam/Smallmouth Bass Flow Options Environmental Assessment, which contains four potential options designed to disrupt the establishment of smallmouth bass.

These flow options were developed collaboratively with the Grand Canyon Monitoring and Research Center, the Smallmouth Bass Task Force, and “technical experts from various agencies using existing research and monitoring data within the Glen Canyon Dam Adaptive Management Program,” the assessment states.

The four primary flow options presented and analyzed in the draft environment assessment combine releasing cold water through bypass tubes and penstocks. In bypass tubes, water moves from the reservoir to the river without passing through the power plant. Comparatively, water flows through penstocks to the power plant’s turbines.

Flow Option A would involve releasing cool water from both penstocks and bypass tubes to maintain an average daily temperature of fewer than 16 degrees Celsius, according to the assessment.

The amount of water released will vary throughout the year, with as little being released as needed to reach temperature goals, depending on availability.

Flow Option B would work similarly to the previous option with the addition of up to three 36-hour flow spikes between late May and mid-July, should sufficient water be available.

During a flow spike, a high volume of water — up to 45,000 cubic feet per second — would be released through the penstocks and bypass tubes.

For Flow Option C, the minimum amount of water required to create a cold shock — a sudden temperature drop to below 13 degrees Celsius — would be released through the bypass tubes over at least 48 hours, the assessment states.

This option would be initiated once the Little Colorado River area’s daily water temperature reaches 16 degrees Celsius and continue weekly for approximately 12 weeks.

In addition to a cold shock, Flow Option D would initiate up to three 36-hour flow spikes, similar to the second option.

While the flow actions contained in the assessment “represent the most effective options for preventing the immediate establishment of smallmouth bass” below the Glen Canyon Dam,” additional work will be required, bureau public affairs officer Becki Bryant wrote in an email.

“We will continue to work with our stakeholders and partners to identify actions to discourage the establishment of nonnative species,” she wrote.

The 14-day public comment period, ending March 10, allows for the public to review the environmental assessment and identify additional issues or concerns, Bryant said. Once the comment period ends, submissions will be reviewed and considered as the agency prepares a final draft.

The finished environmental assessment is expected to be published this spring, and should it receive a finding of “no significant impact,” the plan would be implemented around June 1, Bryant wrote.

To read the environmental assessment, click here. Those interested in submitting a comment can do so via email.

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