What Causes Fish Kills: Common Causes & Prevention

By Debbie Hanson

Nov 23, 2020

What causes fish kills, how to report a fish kill to your state agency, contribute to conservation by doing your part to prevent harm to aquatic environments 

Part of taking an active role in the conservation of our nation's fisheries means understanding how you can help protect and preserve our natural ecosystems. This includes learning about what causes fish kills, reporting a fish kill if you see one, and taking action to prevent harm to our aquatic environments whenever possible.

What Causes Fish Kills?

If you're wondering what causes fish kills in lakes, ponds, rivers, streams, and oceans; there isn't just one answer, but the most common cause is a lack of oxygen in the water. The lack of dissolved oxygen may be due to factors such as drought, algae blooms, overcrowding, or a sustained increase in water temperature, but can also occur as a result of human activity that adds nutrients, such as nitrogen and phosphorus, to our waterways (nutrients that can come from fertilizers, automobiles, sewage, and other sources).

However, fish kills not only occur when there is a lack of oxygen in our aquatic environments, they can also take place when toxic compounds are released into a body of water, or due to infectious diseases and parasites.

Reporting a Fish Kill

When you come across a fish kill, it's very important that you report it to your state fish and wildlife agency. The information you provide will help scientists and biologists study disease and mortality in fish populations, and help them respond to fish die off events.

If you're wondering how to report a fish kill, you should contact your state fish and wildlife conservation agency. State agencies usually have a toll-free number set up for this purpose. These toll-free hotlines provide information about how and where to report fish kills, fish with parasites, or other fish abnormalities.

Conservation and Prevention

Now that you have more information about what causes fish kills and how to report a fish kill, know that there are specific steps you can take to help prevent them. First, use natural, slow-release nitrogen, or low phosphorus fertilizers around your home or garden, and be sure to follow the instructions on how to correctly apply them. Second, don't apply fertilizers or pesticides before it rains. Third, when considering the landscaping around your home, use drought-resistant native plants that require less fertilizer and less water.

When fertilizers or pesticides are improperly applied, they can wash off your lawn or garden into storm drains and end up in our lakes, rivers, and the ocean. These chemicals can cause algae blooms, in addition to being toxic to our natural wildlife and plants.

By making small changes in our daily habits, we can contribute to conservation and the prevention of pollution and fish kills.

Debbie Hanson
Debbie Hanson
Debbie Hanson is an award-winning outdoor writer, women’s sport fishing advocate, IGFA world record holder, and freshwater guide living in Southwest Florida. Hanson’s written work has appeared in publications such as Florida Game & Fish Magazine, BoatUS Magazine, and USA Today Hunt & Fish. To learn more about her work, visit shefishes2.com or follow her on Instagram @shefishes2.