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The recent rains and cloudy skies are causing problems along the Withlacoochee River and in lakes around Citrus and Sumter counties.
Residents are reporting fish kills in various areas, and Fisheries Biologists with the Florida Fish and Wildlife Conservation Commission (FWC) think the number and severity of fish kills could increase over the next several weeks.
“We’ve already had reports of fish kills in the Inverness and Floral City areas as well as various locations on the Withlacoochee River. These kills are a result of low dissolved oxygen (DO) levels,” said Allen Martin, regional fisheries biologist for the FWC’s Division of Freshwater Fisheries Management in Lake City. “And it could get worse in the coming weeks if we get tropical storm or hurricane activity.”
What do heavy rains and cloudy skies have to do with fish suffocating from a lack of oxygen?
Ironically, a lack of sunshine in the Sunshine State heralds the beginning of problems. The process starts with overcast skies, hot summer days and rainy weather.
Photosynthesis creates most of the oxygen that fish breathe. The process allows waterborne microscopic plants to use sunlight to produce and add dissolved oxygen to the water. However, when overcast skies persist for several days, there is often not enough sunlight to power the oxygen-making process that supports fish life.
Heavy rain and wind from thunderstorms add to the problem by stirring up bottom sediments that mix with good-quality water near the surface, compounding the problem. Rainwater runoff can also wash large amounts of decaying plant and animal material into the water body. In the decay process, bacteria use dissolved oxygen in the water to break down plant and animal matter, further lowering oxygen levels.
“We are seeing this occur in the Green Swamp area,” Martin said. “The rains are releasing a pulse of poor-quality (low DO) water into the Withlacoochee River that is then flowing into the Tsala Apopka chain of lakes.”
Fish can often be seen coming to the surface of the water and gulping air. Ultimately, the fish die and float to the surface.
“The size of the fish kills depends on how low the oxygen levels are. They can range from only a few individuals being affected to massive kills, where thousands of fish die.”
Many different species of fish have succumbed to current fish kills, including largemouth bass, bluegill, black crappie and catfish.
The good news is that most water bodies do not suffer repeat performances every year. In fact, most water bodies go years without suffering a major fish kill. Fish populations usually replenish themselves naturally from surviving fish.
“In spite of summer fish kills, most Florida lakes are in relatively healthy shape, and fish populations remain stable. Angling success generally is not affected over the long haul, even after events that might appear serious to the untrained eye,” said Martin.
Still, it is important for biologists like Martin 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.
Floridians can report fish kills in natural water bodies to the FWC’s Fish Kill Hotline at 800-636-0511, the FWC’s Lake City office at 386-758-0525 or online at MyFWC.com/Contact. It is not necessary to report fish kills in man-made retention or private ponds.