Lake Powell is 23% full — a level that would have seemed unthinkable a generation ago. What was once one of the largest reservoirs in North America has shrunk steadily under the combined weight of overuse, evaporation, and a warming climate, leaving the Colorado River system stretched thin across seven states and 40 million people.
At the center of that pressure stands Glen Canyon Dam. Built to generate power, it now faces a harder assignment: managing a river in crisis. A federal decision expected within weeks could force the dam to choose between its turbines and the cold, deep water that may be the last reliable defense for an endangered fish — and the bill for that choice is already landing on electricity customers across the Southwest.
A reservoir in freefall
Lake Powell’s decline is not a sudden crisis. It has been building for decades, as overuse, rising evaporation, and persistent drought driven by climate change have drained the reservoir to just 23% of its capacity. Record low inflows this summer are expected to push that figure even lower.
Less depth in the reservoir changes how the dam operates. Warmer surface water gets pulled directly through the hydropower generators and sent downstream into the Colorado River — a temperature shift with consequences that extend well beyond the dam itself.
Seven U.S. states, tribal nations, and Mexico all depend on the Colorado River system, and more than 40 million people rely on it for drinking water, agriculture, and energy. Long-term agreements on how to share the river’s dwindling supply have not yet been reached. The current guidelines expire this year.
How warm water becomes a predator’s ally
Smallmouth bass were introduced into Lake Powell in the 1980s for sport fishing. They thrive near the warm surface layer of the reservoir — the same water pulled through the generators. A recent study found that roughly half of the bass survive that passage and enter the river below the dam.
Water temperatures just downstream of Glen Canyon Dam are projected to consistently exceed 60°F (15.5°C) by mid-June, the threshold at which non-native fish can reproduce. If bass establish themselves below the dam, they gain access to the Grand Canyon — a 278-mile stretch historically protected from this particular threat.
The humpback chub, a federally threatened native species, already faces heavy predation pressure in upper sections of the river. Agencies spend millions of dollars each year removing bass there. Cool water releases in 2024 and 2025 successfully prevented spawning below the dam, but no permanent physical barrier exists to stop bass from passing through the generators.
The mechanics and cost of a ‘cool mix flow’
A cool mix flow works by releasing cold water from deep within Lake Powell through jet tubes, bypassing the turbines entirely. Those turbines sit near the warmer surface layer, so routing water around them sacrifices power generation in exchange for lower downstream temperatures. The tradeoff is straightforward — and expensive.
If approved, the release would run from June through October, cutting roughly half of Glen Canyon Dam’s power output during that period. Utilities would need to purchase replacement energy on the open market, almost certainly at higher prices.
The 2024 numbers illustrate the scale: nearly 900,000 acre-feet of water bypassed the generators, resulting in $19 million in replacement energy costs, according to the Bureau of Reclamation. This year’s cost is projected at around $25 million. A decision is expected within weeks.
Utilities and ratepayers feel the squeeze
About 155 utility customers purchase federal hydropower from the Colorado River system through the Colorado River Energy Distributors Association. The association opposes the cool mix releases and has questioned whether $20–$30 million per year in remediation costs is a sustainable approach.
In a letter to Interior Secretary Doug Burgum, the association warned that the releases threaten a critical fund used to operate, maintain, and invest in hydropower and transmission infrastructure — describing them as an unsustainable response to a problem with no permanent fix.
The financial strain shows up at the customer level. Heber Light & Power in Utah has raised rates for five consecutive years, partly because of declining hydropower output from Lake Powell. One Heber City resident watched her April electricity bill climb from $86 to $126 over two years. Late payments at the utility have risen from 10% to 12%.
A world-famous fishery on the edge
Dave Foster has worked on or around Marble Canyon — the stretch of river between Glen Canyon Dam and the Grand Canyon — since he was 13 years old. He remembers the 2022 warm-water event clearly. It killed nearly half the rainbow trout in a fishery that draws anglers from around the world.
Three years later, the population still hasn’t fully recovered. Cool water releases in recent years have helped prevent further losses, but the fishery remains fragile. Foster has already begun warning customers booking trips after mid-June that he may have to cancel if water temperatures climb too high.
His read on what happens without cool releases this summer leaves little room for interpretation. “That’s it for the trout fishery,” he said. “There’s no ambiguity about it. It will destroy it.”
The coming weeks will determine whether that outcome can be avoided. The Bureau of Reclamation’s decision will set the terms not just for this summer, but for how the region navigates an increasingly difficult set of tradeoffs — between power generation, endangered species recovery, and the livelihoods tied to a river that fewer people can afford to take for granted.
Carlos is an engineer with strong expertise in technical and industrial topics. He previously worked at international companies such as Siemens and speaks Spanish, German, English, and Italian.
