News Releases

Fish kills common this time of year

News Release

Friday, July 23, 2010

Media contact: Carli Segelson, 727-896-8626

High temperatures and cloudy rainy days can spell trouble for fish in Florida's rivers and lakes. These conditions can cause fish kills, which are natural occurrences and typically do not cause permanent damage to the ecosystem or to fish populations.

Many factors can contribute to a fish kill. Some fish kills are complex and involve a variety of factors that may not be easily discernable. However, most common causes of kills in brackish estuaries, freshwater lakes and man-made retention ponds are well understood by scientists.

Fish kills are commonly caused by weather-related factors. Sudden temperature fluctuations or extreme temperatures can result in fish kills any time of the year. Hot weather during the summer months can cause fish kills because warm water holds less oxygen than cold water. In addition, a lack of rain during hot-weather months lowers the water levels in the system, heating the water and further depleting the oxygen in the system.

Fish kills also can occur during extended periods with little sunshine. The process leading to these types of die-offs begins with overcast skies and rainy weather. During extended periods of overcast, rainy or cloudy weather, the biological system uses the dissolved oxygen in the water faster than it can produce it.  Rain water can compound the situation by causing vegetation, such as dead leaves and grass clippings, to wash into the system and decompose. The decomposition process also can remove oxygen from the water.

The good news is that most natural water bodies are resilient to these types of fish kill events.

It is important for Florida Fish and Wildlife Conservation Commission (FWC) scientists to keep track of the location and extent of fish kills in natural lakes and estuaries to see if there are serious problems developing in an ecosystem that might require investigation or restorative measures.

Residents can report fish kills in natural water bodies to the FWC at the FWC Fish Kill Hotline at 800-636-0511. It is not necessary to report fish kills in man-made retention or private ponds to the FWC.