There’s one species of alga in the Brazos River Basin that’s caused documented toxic events. It shares a name with that ‘Golden’ hit by from KPop Demon Hunters, but you won’t find any fans of this version.
Golden alga, or Prymnesium parvum, is one type of microscopic alga frequently present in low concentrations in the rivers and lakes within the basin year-round. Golden alga is usually harmless.
But, this alga is unique from other forms found in the basin in the worst way.
It has toxic blooms.
These aren’t pretty, colorful blooms that feed the bees. These blooms occur when the alga enters a phase of rapid growth and reproduction. The toxins can kill species with gills, think, fish, freshwater mussels and clams, and the gill-breathing juvenile stage of frogs and other amphibians, according to the Texas Parks and Wildlife Department (TPWD).
"There is no evidence that golden alga toxins pose a direct threat to humans, other mammals, or birds.
Still, people should avoid picking up dead or dying fish for consumption.”
– Texas Parks and Wildlife Department
In 2003 and 2005, the freshwater organism nearly devastated some fish populations in lakes Possum Kingdom, Granbury, and Whitney in the Brazos River Basin and many other Texas lakes outside the basin.
Golden alga can occur in all types of water bodies, but those harmful events typically occur in brackish or salty water. And those blooms tend to occur in cold weather.
A fish kill resulting from golden algae can last for days, weeks, or months. It can affect whole water bodies or just isolated portions. If you live lakeside, or hang out by the water during the few cooler months we get in Texas, and you see water that appears brownish or tea-colored, you could have spotted a bloom. Foaming could occur when there’s a lot of wind. But there are other, more likely indicators that no one enjoys coming across.
A toxic golden alga bloom could be occurring if you see fish gulping for air at the water’s surface, fish swimming in irregular patterns or manners, often appearing intoxicated, or visible hemorrhaging in the fish, which can give the fish a pink to red appearance.
Small fish are typically hit first. Larger fish are impacted if the toxic bloom lasts too long, expands, or increases in intensity.
If you see any of these signs, it’s super important to quickly notify the Brazos River Authority. Don’t wait. A quick notification can help successfully determine the cause of a fish kill. 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.
The BRA has a Harmful Algal Bloom (HAB) reporting site available to the public. If you think you may have come across a fish kill, fill out the date and time of the observation, where you saw it, and any specific details you noticed, such as the color of the water, if there’s a smell, if the water seems to have a certain texture, or if you see dead fish. Don’t forget to include how many fish you see. If you know the types of fish, even better.
The Texas Parks and Wildlife Department also has a 24-hour number you can call instead if that’s quicker and easier: 512-389-4848. Quick reporting is also important because evidence of a golden alga-related fish kill is often difficult to track. Birds and raccoons could take off with the dead fish before they are counted. Also, dead fish tend to sink quickly, which makes it hard to see the impact.
The TPWD keeps a running list of Golden alga bloom reports here: Golden Alga Current Bloom Status
Golden alga was first confirmed in West Texas in 1985, though descriptions of fish kills go back to the 1950s, according to the TPWD.
Unfortunately, to date, there is no effective tool to control Golden alga in large reservoirs and rivers, according to TPWD. Research is ongoing to explore potential control or management actions.
“The dynamics of bloom formation still aren't well understood. Golden alga can live in a water body for months, even years, without causing a fish kill. Scientists suspect that a number of factors — temperature, water chemistry, rate of stream flow — combine to give golden alga an advantage over other plankton species and lead to a population explosion.” – Texas Parks and Wildlife Department.