Blue-Green Algae (cyanobacteria)
Cyanobacteria are commonly called “blue-green algae” or “pond scum,” but are actually not algae at all. They are a group of photosynthetic bacteria. Like true algae, blue-green algae do make up a portion of the phytoplankton in many waterbodies. However, unlike true algae, they are generally not eaten by other organisms and are not an important part of the food chain.
There are more than 2,600 species of blue-green algae. Most blue-green algae are not known to produce toxins.
When blue-green algae end their lifecycle, they emit an oily substance called geosmin, which has a distinctive earthy taste that humans can detect in even small concentrations. The woody, musty, earthy taste that shows up from time to time in our drinking water is normally due to the die-off of a portion of a waterbodies population of the algae.
While this added flavor in drinking water can be annoying, it poses no health hazard.
While most blue-green algae are not harmful to animals, some types have the potential to produce toxins that are harmful to aquatic organisms such as fish, and in some cases, humans, pets, livestock and wildlife.
There are two types of blue-green algae, Anabaena sp. and Microcystis sp., known to occur in Texas that can produce toxins.
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.
Other environmental concerns that can be caused by blue-green algae include discolored water, reduced light penetration, and dissolved oxygen depletion.
An algal bloom is a sudden, massive growth of microscopic and macroscopic organisms that develop in surface water. Fortunately, there have not been any recorded toxic blue-green alga blooms in the Brazos River basin in more than 25 years.
If you’re on a water body, you will be able to tell there is an algal bloom; however, you wouldn’t be able to tell which type of algae it is unless you look at it under a microscope. Experts advise that if you see water with a “pea-soup” color and consistency, avoid it.
Fish kills can have many causes, and toxic blue-green algae blooms are just one.
When there is a report of dead fish in the Brazos River basin reservoirs or rivers, the BRA’s environmental team will assist the Texas Parks and Wildlife Department’s Kills and Spills Team in documenting the event and investigating the cause.
No matter the cause, there are also good standard practices any time dead fish are in your area. Good practices include not swimming near dead or dying fish and not eating dead or dying fish. Only eat fish that appear healthy at the time they are caught.
If you see a fish kill on the Brazos River or anywhere in the state, call the Texas Parks and Wildlife Department’s 24-hour communication center at (512) 389-4848 or email firstname.lastname@example.org.
Prompt notification is key to successfully determining the cause of a fish kill.