CPW asks anglers to fish outside of the hottest times of the day to reduce stress on fish.

It's been hot, and as the temperatures rise, so do the temperatures in the state's lakes ... and that's bad news for fish. On Sunday, July 19, a concerned citizen sent a video to CBS 11 News in Colorado Springs showing nearly 100 dead fish on the banks of Prospect Lake. 

City officials and Colorado Parks and Wildlife (CPW) say that the fish die-off is most likely due to the high temperatures warming up lake water beyond what fish can handle. In addition, Prospect Lake closed in June due to blue-green algae, which might have also played a part. 

According to CPW, heat, drought, and low water levels are contributing to elevated water temperatures in much of Colorado, depleting oxygen levels and leaving trout vulnerable. Trout function best in 50-60 degree waters, so when temperatures exceed 70 degrees, they often stop feeding and become more susceptible to disease.  Warm temperature and low water levels can also lead to algae blooms in rivers and reservoirs, which cause oxygen levels to drop when algae die and decompose.

To help reduce stress on fish this time of year, CPW is asking anglers to fish early in the morning or in the high country where temperatures are generally lower. They are urged to carry a thermometer to monitor water temperature, as well.

“Anglers should monitor water temperatures and end their trout fishing adventures when water temperatures start to approach 70 degrees,” said Matt Nicholl, CPW’s Aquatic Section Manager. “If trout have difficulty recovering after being caught and are acting lethargic, it’s a good decision to call it quits for the day.”

Other tips to reduce stress on fish when the weather is hot include:

• Using a heavier tippet and line to quickly reel in and release the fish. 
• Using barbless hooks to reduce the time required to unhook the fish (when fish are hooked, their metabolic rate and oxygen consumption soar, greatly increasing their risk of disease and death).
• Wet hands before handling fish.
• Keep the fish submerged while unhooking and releasing it.
• Avoid taking the fish out of the water even for a quick photo in these conditions.

CPW hasn't issued any fishing closures, but it could do so to protect aquatic resources from severe fish mortality or detrimental impacts to fishery resources as a result of sub-optimal water conditions. To check for fishing closures, call your CPW regional office.