Fish kill likely attributed to weather

Thousands of dead fish were found floating on the surface of Lake Apopka starting Jan. 31, prompting several state agencies to conduct tests to try to find the cause.

Officials with the Florida Fish and Wildlife Conservation Commission pulled dead fish out of the lake for testing Monday, Feb. 3, and still are waiting for the results. The Department of Environmental Protection and the St. Johns River Water Management District were conducting tests on water samples from the lake. The three agencies are collaborating on the investigation.

Friends of Lake Apopka reported the fish kill on its Facebook page Feb. 4 and said it would pass along new information as it is received.

Joe Dunn, FOLA board member, would not speculate on the cause “of this very heartbreaking fish kill, but we should let the knowledgeable scientists at SJRWMD, FWC and DEP thoroughly investigate before we rush to judgment,” he said. “This is not a simple thing to explain.”

Residents have been complaining about the horrible odor emanating from the lake, and several said the smell was so bad their children couldn’t play outside. Folks have been speculating on what happened, blaming algae blooms, cold weather and herbicides.

Piles of dead fish were reported on the lake’s shores at the Oakland Nature Preserve as well.

“This fish kill is very unfortunate,” ONP director Nicole O’Brien said. “A couple of theories are being explored. First is a harmful algal bloom of blue-green algae called microcystis. An algal bloom was reported near Newton Park in Winter Garden in December. We have not observed visual evidence of a bloom near our dock. A (harmful algal bloom) produces toxins that harm the fish and also can cause low dissolved oxygen by blocking sunlight.

“Another theory is that there was a dramatic change in water temperature, which was recorded at data recorders in different parts of the lake,” O’Brien said. “Florida had an extended period of cold weather in January — the coldest January since 2010. Water temperature usually lags air temperature a little, so the water would have remained cold through the end of January. We then seemed to have a significant temperature increase. A dramatic fluctuation in the temperature can cause a shock to the fish, resulting in a die-off.”

Andrew Marbury, a fisheries resource biologist for the Harris Chain of Lakes for FWC, said his agency has been busy trying to get answers.

“We started to get the reports in small amounts probably Friday, Jan. 31, and into that weekend, and that’s really when we saw the bulk of this fish kill happen — from Jan. 31 to about Feb. 2,” Marbury said. “Most of those reports were centered on the southern shoreline of the lake … Winter Garden all the way up to Montverde area. … It was a pretty extensive size event.”

St. Johns and DEP took water samples to look at algae concentrations and toxins in the water, Marbury said. FWC also looked for physical abnormalities in the fish.

He said officials were waiting on the results of the toxin testing. SJRWMD is running the water analyses.

“We do have water-monitoring stations on Lake Apopka, and we were able to pull information from that,” Marbury said. “We saw, for the most part, sufficient water quality … so dissolved oxygen not being the driving factor behind this is likely.”

FWC collected data regarding water temperature as well.

“We were able to see drastic changes in water temperatures over the last two weeks,” Marbury said. “With those two cold fronts we had … Jan. 21 through 24 sometime, we had water get down to about 47 degrees or so, and that’s really cold for Florida. It can kill off species that are exotic, like tilapia, but it also can cause stress to other species that are here in the lake. So that’s something we’re looking at as well.”

The fish kill wasn’t limited to any one species. Marbury reported the affected fish as bass, gizzard shad, blue gill, crappie, tilapia, gar and catfish. The dead fish will not be removed from the lake, he said.

“Generally, nature will run its course and they’ll start to decompose,” he said. “Birds and other fish species and other aquatic animals may end up getting rid of those.”

Some residents were concerned other animals would die if the cause of the dead fish was herbicides, but Marbury responded to that theory: “During this entire two-week period, we do not have any birds, amphibians or other animals (affected), and no other fatalities have occurred.”

The agencies are hoping to receive the testing results this week.

“We don’t see this extent of a kill very often,” Marbury said. “The seasonality of it is also different because it happened in the winter. Most freshwater kills happen in the warmer months, in the summer. It’s definitely odd in that aspect, and the extent to which we’ve seen this fish kill is definitely not something we’ve seen in recent years at all.”