Federal officials said Thursday they will not release cool water this year from one of the Colorado River’s major reservoirs,…Federal officials said Thursday they will not release cool water this year from one of the Colorado River’s major reservoirs, which would have protected a threatened native fish downstream but put more strain on already struggling hydropower production. As the Colorado River and its once massive reservoirs shrink from overuse and climate change, officials were faced with a decision that pits conservation of the humpback chub — a threatened fish native to the river — against ratepayer costs for electricity. A “cool mix flow” is when cold water is released from deep in a reservoir — in this case Lake Powell — to cool the river below. With such a low reservoir, warm water near the surface gets sucked through the generators and sent downstream. Officials say cool water releases from Lake Powell in 2024 and 2025 successfully prevented smallmouth bass spawning.