Harmful Algal Blooms
Many types of algae occur naturally in all surface water in Texas.
Algae is a base organism in the aquatic food pyramid.
Alga are photosynthetic, meaning they harness energy from sunlight and turn
it into chemical energy. Any number of the different types of Algae may exist
in one waterbody at the same time.
While most algae are not problematic, some types have the potential
to produce toxins that are harmful to aquatic organisms and, in some
cases, also harmful to humans, pets, livestock and wildlife. Toxic
algae events are called “blooms.”
Harmful Algal Blooms
The word “bloom” may remind you of springtime and flowers;
but, harmful algae blooms do not produce flowers. They can
discolor the water and produce scum or foam, but during this process, they grow out of control, producing harmful toxins.
An algal bloom is a sudden, massive growth of microscopic
and macroscopic organisms that develop in surface water.
The rapid growth is often associated with water bodies with
abundant nutrients. Blooms can occur in warm freshwaters,
marine waters or brackish waters and are often associated
with water bodies with ample nutrients.
A harmful algal bloom occurs when an alga capable
of producing toxins that can cause harm to aquatic
organisms, animals or people grows rapidly.
Harmful algal blooms are becoming more frequent
with climate change, according to the Centers for
Disease Control and Prevention. Water bodies with
an ongoing bloom may look blue, green, brown, yellow,
orange, or red.
Golden algae, or Prymnesium parvum, is one type of microscopic alga that is frequently present in the waters of the Brazos basin in low concentrations.
In the Brazos River basin, there have been numerous documented
golden algae blooms, a few that nearly decimated the fish populations
at Possum Kingdom Lake, Lake Granbury and Lake Whitney in 2003 and 2005.
There have also been blooms that were localized, causing smaller, isolated fish kills.
While golden alga is frequently present in the waters of the Brazos basin
in low concentrations, it is most likely to bloom, becoming toxic, and cause
fish kills in cold weather. A golden alga fish kill may last for days, weeks
or months, and may affect whole water bodies or isolated portions of water
bodies. To learn more about golden algae, go
Red Tide Algae
Red tide is an algal bloom that occurs mostly in the Gulf of Mexico and associated estuaries,
where freshwater from rivers flows into the Gulf, mixing with salt water. While rare in Texas,
red tide events have occurred in Galveston Bay near the Brazos basin estuary. Red tide blooms
occur mostly in late summer or early fall and cause the water to appear to be red to brown in
color. Toxic red tide events not only result in fish kills but are also harmful to humans,
pets, livestock and wildlife.
Cyanobacteria are commonly called “blue-green algae” or “pond scum”, but are actually not an algae at all.
Most blue-green algae, also called cyanobacteria, are not known to produce toxins;
but, there are two species, Anabaena and Microcystis, both known to occur in Texas,
that can produce toxins.
Unlike golden alga, these two blue-green algae species not only cause fish kills
when toxic blooms occur, but their toxins can be harmful to humans, pets, livestock
and wildlife. Blue-green algae blooms are believed to have caused the death of
several dogs in the Austin area in recent years.
To learn more about blue-green algae, go
Effect on Humans
The human illnesses caused by harmful algal blooms, though rare, can be debilitating or even fatal, according to the National Oceanic and Atmospheric Administration. To date, there have been no known, documented algal blooms in the Brazos River basin that were considered harmful to humans, pets or wildlife in the past 25 years.
How do these blooms cause harm?
According to the Centers for Disease Control and Prevention, a harmful algal bloom can cause harm by:
- Producing toxins that can poison humans, fish, seabirds, aquatic animals, livestock, wildlife, and household pets that are near the water, drink the water, or swim in the water.
- Causing illness when a person or animal eats fish or shellfish contaminated with algal toxins.
- Becoming dense enough to keep sunlight from reaching the lower depths of the water.
- Removing the oxygen from the water as it decomposes, starving fish and plants of oxygen, and damaging the local ecology.
Protecting yourself from harmful algae blooms
If you’re on a water body, you will most likely be able to see an algal bloom, but you will not be able to tell which type of algae it is unless you look at it under a microscope.
Some of the signs of an algal bloom are:
- a strong odor
- discolored water
- algal mats or scum floating on the surface
- dead fish or other dead animals
Experts advise that if you see water with a “pea-soup” color and consistency, avoid it. Do not boat or swim near a suspected algae bloom.
The Brazos River Authority environmental services team tracks harmful algae blooms in the Brazos River basin.
If you’re out on a BRA reservoir and notice water that appears green and thick or has an abnormal odor, don’t swim or let your pet go into the area. Do not catch and consume fish that have been caught in the area of an algae bloom.
If you feel you may have spotted an algae bloom, please contact the BRA at (888) 922-6272 with the location.
For more information on harmful algal blooms, go to:
here to learn more about the species of interest and
here to learn about invasive species monitored by the BRA.