Reporter-Herald article: Heat and Drought Drive Major Fish Kill at Horseshoe Lake

 By Jocelyn Rowley | Loveland Reporter-Herald

Originally Published: August 5, 2026

At a Glance

• Location: Horseshoe Lake (flowing into the Boyd Lake inlet).

• Cause: Extreme heat, low water levels, and severely depleted oxygen levels.

• Impact: Thousands of fish lost (primarily common carp, along with walleye, white bass, shad, and catfish).

• Boyd Lake Status: CPW confirms Boyd Lake’s existing fishery remains unaffected and safe.

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For months, Bill Prater watched Horseshoe Lake slowly disappear.

From his home a few hundred yards away, the past president of the Loveland Fishing Club saw the privately owned reservoir shrink into a patchwork of isolated pools as places that had held water earlier in the summer gradually became mud flats.

So he wasn’t naturally surprised when the lake’s fish began dying and floating through the inlet to Boyd Lake.

“The lake is essentially emptied, and that’s when the die-off really took hold.”

— Bill Prater, Loveland Fishing Club Past President

What followed was dramatic, but not entirely unexpected in a summer marked by prolonged heat and dwindling water supplies.

Colorado Parks and Wildlife (CPW) officials estimate that thousands of fish died in Horseshoe before entering the Boyd Lake channel, creating a startling—and increasingly unpleasant—scene that quickly spread across social media. Most of the dead fish were common carp, with smaller numbers of walleye, white bass, shad, and catfish.

Permit Delays and Failed Relocation Efforts

Because Horseshoe Lake is privately owned, CPW does not manage or stock its fishery and did not investigate the conditions that caused the die-off. The Greeley-Loveland Irrigation Company manages water levels within the irrigation system that connects Horseshoe and Boyd lakes. The ditch company could not immediately be reached for comment.

AJ Macdonald, president of the Horseshoe Lake homeowners association board, provided an email sent to residents within the HOA. The email noted that the board reached out for help in saving the fish population after learning that the irrigation company intended to draw the lake down to such a low level.

After contacting the ditch company and CPW, and learning that saving the fish was not deemed a high priority, the board reached out to the fish farm that originally stocked Horseshoe Lake. Together, they developed a plan to relocate the fish and restock the lake the following year, applying for a state permit to proceed legally.

“The owner of the fish farm was assured by the state that our permit would be approved last week and that they could start moving fish immediately,” the HOA email stated. “No action has been taken as our permit has still not been issued. Unfortunately, now all our fish have died.”

CPW crews were able to salvage some live fish remaining in the inlet, relocating them to another body of water that already contained carp. The remaining carcasses will largely be left in place.

Agency representatives emphasized that the fish did not die in Boyd Lake and that Boyd's existing fishery has not been affected.

“There’s just dead fish that flowed into the inlet,” said CPW Public Information Officer Kara Van Hoose. “There’s not a lot you can really do.”

The Science Behind the Die-Off: Temperature and Oxygen

Although the exact cause of the Horseshoe Lake fish kill has not been officially confirmed, experts say prolonged heat and shrinking water supplies create conditions that make die-offs far more likely across Colorado.

“The hotter the water is, the less oxygen it naturally holds, and, at the same time, the hotter the water is, the more oxygen fish use,” explained Chris Myrick, a Colorado State University professor of fisheries and aquatic sciences. “So it’s a double whammy.”

When a lake shrinks, fish become concentrated in a much smaller volume of water, compounding the demand on a dwindling oxygen supply.

“You have a limited amount of water, a limited amount of oxygen, and fish that are using a lot of oxygen even when they’re resting,” Myrick said. “Then you just run out of oxygen.”

Myrick, who did not inspect Horseshoe Lake personally, cautioned that confirming the exact cause of a fish kill normally requires water-temperature and dissolved-oxygen measurements taken directly at the site. Investigators may also test for chemicals, toxic algae, or other environmental stressors.

However, he noted that the frequency of fish kills and emergency salvages around Colorado this summer is logical given the conditions.

“I think this year it’s been exacerbated by starting off with relatively low water levels in some of the reservoirs,” Myrick said. “And then high temperatures just make it worse.”

Ecological Impact and Looking Ahead

The dead fish themselves are unlikely to pose a danger to Boyd Lake’s surviving fish or nearby wildlife, according to Myrick. Unless toxic substances caused the deaths, carcasses are routinely left in place for scavengers to consume or to decompose and recycle nutrients back into the ecosystem.

That natural process, however, has made the inlet a tough place to visit recently.

Dead fish have collected in shallow water and along the exposed lakebed, where a few remaining fish could still be seen swimming among carcasses earlier in the week. As decomposition set in, the piles produced a severe odor, Prater noted.

The scene has also drawn an array of hungry birds, including herons and gulls, taking advantage of the easy feast.

“If you’re a birder, you’ll be able to see all kinds of them,” Prater said.

With high temperatures continuing throughout the region, local anglers should keep an eye on water conditions across northern Colorado. Prater noted signs of stress among fish in other local spots and warned that additional lakes could face similar vulnerabilities if hot, dry conditions persist.

“This might not be the end of it,” he said.