St. Johns River Fish Kills

Update as of 7/23/10:

Dead fish and cyanobacteria bloom

Based on preliminary results, including the findings from water testing performed by scientists at the University of North Carolina Wilmington, a primary hypothesis for the fish kill is that the kills were caused by low level toxins in the St. Johns River. In the few fish specimens tested so far, researchers observed significant effects in the internal organs, with damage to the heart, liver, pancreas, kidney, and brain. In addition, the red blood cells in the fish appeared to be destroyed by a type of toxin known as a hemolysin. This toxin can be produced by algae, bacteria, or chemicals in the water, or by pathogens (e.g. bacteria that cause disease) that infect fish.

Even though the fish kill is over, Florida Fish and Wildlife Conservation Commission (FWC) scientists are continuing to conduct multiple tests to try to determine the source of the hemolysin. These tests include examining some bacteria and algae that were present in the river to see if they produce the toxin, as well as conducting an experiment at the FWC's marine hatchery to assess whether the toxin is passed through the marine food chain from menhaden to red drum.

About this event:

In late May 2010, the FWC began receiving reports to the FWC's Fish Kill Hotline of dead and dying fish in the lower St. Johns River, including Lake George. Water observations were normal and citizens making the reports did not observe lesions or sores on the dead fish. Water samples obtained at the beginning of the event indicated that high concentrations of a harmful algal bloom cyanobacterium (blue-green alga) species, Aphanizomenon cf. flos-aquae, generally co-occurred in the same area as the fish kills. These blooms did not contain elevated concentrations of algal toxins.

In the weeks that followed, the FWC and its partners continued to receive reports from throughout the St. Johns River and Lake George. Through the first week of July 2010, the FWC received over 316 reports about fish kills, dying fish, discolored water, and algal blooms. In response, the FWC worked with multiple groups and partners to investigate the fish kills and share information. The groups and partners involved included the St. Johns Riverkeeper, the St. Johns River Water Management District, the City of Jacksonville's Environmental Quality Division, the Coastal Conservation Association, the Florida Department of Health, and the Florida Department of Environmental Protection. Working with these organizations, the FWC collected water samples for harmful algae, toxins, and bacteria analysis, as well as dying fish for necropsy (an examination of dead fish) and pathology (study of diseases and their causes). The investigation focused on a stretch of the river approximately 30 miles in length extending north from Magnolia Point to Tallyrand (downtown Jacksonville), as well as an area further south in Dunns Creek and Lake George.

FWC staff members from multiple office locations, including Jacksonville, Eustis, DeLeon Springs, and St. Petersburg, were involved in collecting samples from the affected areas. FWC staff members in St. Petersburg received approximately 50 fish that were suitable for running diagnostic tests. The fish received included red drum, menhaden, longnose gar, Atlantic stingray, and white catfish. These species were reported to be the most affected during the event. The processing of these fish samples for disease diagnostics can take several months to complete.

By the second week of June, Aphanizomenon cf. flos aquae became less dominant in the lower St. Johns River, in part because of an influx of low salinity (slightly salty) water that restricted the growth of this alga. Water samples collected in the first half of June from the St. Johns River, including samples taken from Dunns Creek and Lake George, contained a variety of cyanobacteria including Aphanizomenon cf. flos-aquae, Microcystis, Anabaena, and Pseudanabaena. The blooms of these various blue-green algae species continued for a few weeks, dominating different areas of the St. Johns River, and causing low dissolved oxygen levels in shallow or narrow areas, such as canals. In these areas, the fish died because of poor water quality conditions, such as low dissolved oxygen. However, low dissolved oxygen is not believed to be the primary cause for the large-scale die-off of fish.

Throughout this investigation, researchers observed that this was not a typical fish kill event. This fish kill event differed from more typical situations in that not all species of fish appeared to be affected. Also, the kill continued for more than a few weeks with fish dying slowly, while water quality tests indicated generally normal conditions in the river. The symptoms and pathology observed in the fish were different from those commonly observed in fish from rapid kill events. This was a progressive and slow fish kill where conditions were changing over time, making it more challenging to determine a primary cause.

FWC researchers continue to process and analyze samples either collected by or submitted to FWC's Fish and Wildlife Research Institute in St. Petersburg as part of the ongoing investigation into the cause of the St. Johns River fish kills. However, attributing a single cause to a fish kill is not always feasible, as the cause can potentially involve a variety of factors that include water quality, harmful algal blooms, weather conditions, contaminants or pesticides, and other environmental factors.

Please contact the FWC Fish Kill Hotline at 1-800-636-0511 to report any diseased, dying, or dead fish. Continued reports from the public help provide location information and allow researchers to assess whether the fish kills are reoccurring.