Recently, the issue of blue-green algae (cyanobacteria) and
their potential impacts to the environment, natural resources, and
public health has earned much attention in the USA. Common in most
of Florida's aquatic environments, many cyanobacteria species are
capable of producing harmful toxins (cyanotoxins). Cyanobacteria
can cause unsightly blooms; cause taste and odor problems in public
water supplies and can kill domestic animals, pets, and fish and
wildlife that drink or are otherwise exposed to untreated
contaminated water or toxic biota.
Although a major focus for public health officials is
cyanotoxins in drinking water supplies, increased concern for the
possible risk for human illness through recreational exposure is on
the rise. In 2005, the Florida Department of Health (
DOH) issued health advisories recommending people and their
pets refrain from recreational use or contact with blue-green algae
blooms in both the St. Johns River (Duval, Clay, and St. Johns
counties) and the St. Lucie River (Martin County from the
Okeechobee Canal to the St. Lucie Inlet).
In recent years, publicity over blue-green
algae in central Florida lakes, the St. Johns, St. Lucie, and
Caloosahatchee rivers, has led to the FWC receiving enquiries from
the public concerned about human health risks and whether fish are
safe to eat from affected areas.
Cyanobacterial blooms are common in Florida lakes, rivers,
streams, and ponds. Approximately 20 cyanobacteria species in
Florida's waters are capable of producing toxins, including bloom
forming species of Microcystis, Cylindrospermopsis, Anabaena,
Aphanizomenon, Lyngbya, and Planktothrix.
Different cyanobacteria species can produce more than one type
of toxin. As with other harmful algal blooms (HABs), cyanobacteria
and their toxins can disrupt and damage sensitive ecosystems, and
threaten public and natural resources health and the
environment. The public may be at risk if they ingest
untreated drinking water from affected areas, or possibly from
recreational exposure to toxins.
Cyanobacteria blooms are most common in the summer when growth
conditions are ideal but may occur at any time of year. There is no
standard duration for a bloom and no way to determine visually
whether or not a bloom is toxic. Persistent blooms affect many of
Florida's largest and most important rivers, lakes, and estuaries
including the St. Johns, St. Lucie, and Caloosahatchee rivers and
lakes Okeechobee, Apopka, Griffin, and Harris.
There are three main types of cyanotoxins in Florida's
freshwater systems: hepatotoxins (affecting the liver), neurotoxins
(affecting the nervous system), or dermatotoxins (causing topical
To date, very few cases of human illness related cyanobacteria
incidents have been reported in the U.S. In Florida's freshwater
systems, some toxic cyanobacteria such as Microcystis,
commonly form blooms that can, on occasion, appear in lakes and
rivers and in reservoir waters destined for drinking water use.
These water treatment plants are designed to remove bad odors and
taste associated with blue-green algae blooms and to extract toxins
from the source water.
Recreational exposure by direct contact with a cyanobacteria
bloom from activities such as jet-skiing, boating, and swimming
have been reported to cause hay fever-like symptoms (itchy eyes,
sore throat, congestion) and dermal reactions (skin rashes,
blistering) at high concentrations. Ingesting contaminated water
can cause gastrointestinal distress (diarrhea, abdominal pains,
nausea, vomiting). Low level chronic exposure of contaminates
through water or fish have yet to be studied.
The risks of cyanotoxins to natural resources remain relatively
unknown. Health problems may occur in animals if they are
chronically exposed to fresh water with cyanotoxins.
Livestock and domestic animals can be poisoned by drinking
contaminated water, and fish and bird deaths have been reported in
Florida water bodies with persistent cyanobacteria blooms.
It is important to remember these toxins have no known antidotes
and cannot be removed by boiling.
The Florida Department of Health (DOH) advocates a common sense
approach to eating fish and participating in recreational water
activities where blue-green algae blooms occur.
To reduce your risk of exposure:
- Avoid scummy, foamy water where algae mats are present (Heavy
blooms often appear as bright or pea green to reddish-brown water,
occasionally with a "paint scum" appearance due to dead algae, and
may emit unpleasant gassy odors.)
- Don't cook with, eat fish from, or drink scummy water
- Do not let your pets or children eat or drink from affected
- Don't eat fish that look unhealthy
- Do not harvest dead or dying fish or shellfish
- Do not swim in, jet ski over, or play near scummy water or
- Do not allow your pets or children to swim in, drink from, or
play near scummy water
- Do not irrigate with scummy water
- Do not use herbicides to kill blooms (this can release the
toxins directly into the water)
- Minimize nutrient runoff and use of fertilizers (this reduces
the risk of a potential harmful bloom occurring)
- If contact with suspect or contaminated water occurs, wash off
immediately and thoroughly with clean water and soap (make sure to
rinse the swimsuit areas and your pets' fur). Consult a doctor if
illness occurs. Contact a veterinarian if your pet suddenly becomes
lethargic or shows signs of poisoning including vomiting, diarrhea,
Report any change in the taste, smell, or color of your public
drinking water to your local utility. You may also contact your
local county health department's environmental health program.
In the event someone suspects they may have become sick from
exposure to blue-green algae, the DOH recommends they call the toll
free Aquatic Toxins Hotline at 888-232-8635. The hotline is staffed
by health professionals 24/7 every day of the year. The DOH
works with doctors to help alert for potential problems after
contact with cyanobacteria (
Aquatic Toxins Program). Early detection helps regulate events
allowing county health departments to place
health advisories into effect.
Blue-green algae blooms along with dead, diseased, or abnormally
behaving fish or wildlife can be reported to the FWC's Fish and
Wildlife Research Institute (FWRI) Fish Kill
Hotline (online) or by phone at 800-636-0511. A biologist will
respond or a recorded message asking callers to leave contact
information and a detailed report.
NOTE: The Fish Kill Hotline should not be used to request dead
fish cleanup, this is the responsibility of local authorities, not
Learn more about the causes and prevention of fish kills.