Colorado Parks and Wildlife is asking anglers to limit fishing as rising water temperatures and low precipitation threaten aquatic life. 

Persistent heat and drought have recently caused temperatures in some rivers to exceed 70 degrees, which significantly increases the mortality rate for catch-and-release trout, the agency said in a Thursday, July 30 news release. 

Late afternoon readings on the Colorado, Rio Grande and Arkansas rivers, as well as some of their tributaries, have exceeded 70 degrees, according to the agency, which said it expects conditions to worsen.

Warm water holds less dissolved oxygen, making it difficult for fish to recover from stress after being caught, the agency said. Parks and Wildlife has already implemented voluntary fishing closures across more than 400 miles of river in the state, including on portions of the Colorado, Eagle, Crystal and Roaring Fork rivers. 

The agency said it may implement mandatory fishing closures if any of the following criteria are met: 

• Daily maximum water temperatures exceed 71 degrees
• Streamflows drop to 50% or less of the daily average
• Fish conditions deteriorate and show visible signs of fungus or stress
• Daily minimum dissolved oxygen levels fall below 6 parts per million

In addition to adhering to mandatory closures, Parks and Wildlife is urging anglers who choose to fish to follow the following practices: 

• Limit fishing to the morning hours before water temperatures peak in the late afternoon
• Minimize fish exhaustion by landing them quickly and keeping them in the water during handling
• Practice proper handling and reduce fish stress by avoiding squeezing, keeping fingers out of gills, removing hooks gently, using heavier tippet and line, using wet hands to handle fish, keeping fish submerged in water while unhooking and releasing, and avoiding removing fish from water for photos.

Parks and Wildlife also advises anglers to avoid crowded areas and to have an alternative fishing spot planned. The agency recommends anglers use a handheld thermometer to test water conditions and move to cooler, higher-elevation waters once temperatures approach 71 degrees.

More information, including a list of current fishing closures, can be found at CPW.state.co.us/fishing.