Annual winter tests for golden alga are ongoing in Brazos River basin reservoirs to help monitor the potential for toxic blooms, which can last from days to months and can kill large amounts of fish, mussels, and clams.
Golden Algae at Possum Kingdom Lake
Golden alga, or Prymnesium parvum, is one type of microscopic alga frequently present in low concentrations in the Brazos River basin waters. This alga is unique from other alga found in the basin due to its toxic blooms. It is the only species of algae in the Brazos River basin to have caused documented toxic events
Given the frequency of wintertime golden algal fish kills, BRA aquatic scientists partner with the Texas Parks and Wildlife Department to take monthly samples during the fall and winter for early detection of potential golden alga issues on Possum Kingdom Lake and Lake Granbury.
Testing results from the January water samples causes "a little bit of concern from one site," said Tiffany Malzahn, BRA environmental and compliance manager. There are three indicators scientists review: the number of golden alga cells in a given volume of water, the presence of toxins in the water, and the percentage of golden alga compared to other microorganisms.
"There are no hard and fast rules with golden algae," Malzahn said. "Every time we think it's figured it out, it does something different. It is really good at defying prediction. Most commonly, numbers in the report greater than 10,000 cells/milliliter cause concern that enough algal cells are present to cause toxic event that will impact aquatic life in the reservoir."
Testing at one location at Lake Granbury near the F.M. 51 bridge had numbers that signified the area needed to be watched, she said. While the cell count report was high, the tests indicated there was also a mixed algal community at the location.
"As long as we have a healthy green alga population, they seem to keep the golden alga population down," she said.
Low temperatures, especially like those currently forecasted across the Brazos River basin, can kill some of the green alga, leaving an opening for the golden alga to bloom, Malzahn said.
"The goldens opportunistic and will take advantage of a weak green algae population," she said.
Meanwhile, Malzahn said, water sample testing at Possum Kingdom Lake looked great. That reservoir is typically a low algae lake, she said. Lake Granbury has a healthy algal community due to nutrients supplied to the reservoir, she said. The nutrient inputs are likely due to fertilizers and organic waste materials carried into the lake by stormwater runoff. People often think if a little fertilizer is good, a lot is great. But that's not the case. Too much fertilizer can hurt a lawn, and other plants and the excess can wash into storm drains and into the river itself. This is especially an issue for those who live along lakes, streams or other bodies of water that receive runoff.
Properly maintained septic systems can also go a long way to not throwing off the healthy aquatic balance in the lake. If you use a septic system, make sure it is properly installed and regularly maintained. Septic systems must also be placed a safe distance from water bodies, wells and other areas where they could seep into water supply.
BRA aquatic scientists collect samples at the two reservoirs and then send those to the Texas Parks and Wildlife Department, which analyzes the content. The TPWD also analyzes water samples collected by TPWD staff from elsewhere in the Brazos river basin.
The one reservoir belonging to the BRA that isn't tested in the winter for golden algae is Lake Limestone because it's never had a golden alga fish kill event, Malzahn said.
"Limestone, despite its name, is a very low mineral lake," she said. "There is not a lot of the minerals out there that golden alga needs to make its toxins."
The toxins produced by golden alga are not known to be harmful to humans, livestock or non-gill breathing organisms. Still, never pick up dead or dying fish or eat them. A visual indicator of golden alga includes brownish or tea-colored water.
In 2003 and 2005, the freshwater organism nearly devastated some fish populations in Possum Kingdom Lake, Lake Granbury, and Lake Whitney in the Brazos basin and many other Texas lakes outside of the basin.
When there is a report of dead fish in the Brazos River basins' 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. If you ever come across a bunch of dead fish in the water, take action and report the kill to TPWD's 24-hour communications centers at 512-389-4848.