The FWC received hundreds of reports about discolored water, algal
blooms, dying fish, and fish kills in the lower St. Johns River,
including Lake George.
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
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.