Fish Kills Increase Due To Warming Waters

MADISON, Wis. – The Wisconsin Department of Natural Resources (DNR) alerts the public that because water temperatures are heating up, anglers may notice more dead fish than usual on their favorite waterbodies. 

Many underlying causes can explain this uptick in fish die-offs during warm weather periods, from pathogens such as bacteria, viruses, fungi and parasites, to environmental issues like low dissolved oxygen levels and thermal stress. The DNR reminds anglers and boaters to report fish kill events to their local fish biologist.

It is important to note any fish kill needs to be thoroughly investigated through coordinated efforts between biologists and fish health staff to confirm the underlying cause. Because dead fish decay quickly in warm temperatures and water conditions can change rapidly, it won’t always be possible to definitively determine the reason for a fish kill. 

Though anglers and boaters may see high numbers of dead or diseased fish as waters warm, know that these events usually do not have a lasting impact on the larger fish population.

The DNR urges anglers and their pets to never consume dead or visibly sick fish. Thoroughly cook any harvested fish and follow the U.S. Food and Drug Administration’s food safety guidelines. 

If you catch a diseased or dying fish or observe a fish kill, please take the following steps: 

• Always wear gloves or wash your hands after handling dead or dying fish.
• Anglers should not actively collect fish samples from a fish kill event. If you accidentally catch a diseased or dying fish, retain the fish as a part of your daily bag limit and place the fish in a plastic bag on ice in a cooler. Do not transport the fish to a DNR office or hatchery.
• Note the waterbody, date, fish species and number of dead or dying fish and report it immediately to your local fisheries biologist or the DNR tip line (1-800-TIP-WDNR or 1-800-847-9367).
• If possible, and it’s safe to do so, take clear images of the affected area (e.g., waterbody showing dead/dying fish) and close-up images of the affected fish.

Your local biologist will contact you as soon as they are able and determine whether the carcass can be collected or how it should be properly disposed of. Please note that due to resources, DNR staff will not be able to visit every potentially diseased caught fish or occurrence of dead fish.