Golden Alga in Texas

Archived News Release

Feb. 17, 2003

Golden Algal Blooms Active in Four Texas River Systems

AUSTIN, Texas — The Texas Parks and Wildlife Department reports active golden algal blooms are affecting fisheries in four major Texas river systems, particularly along the Brazos River. The naturally occurring toxin has caused significant fish kills during the past few weeks in Lake Granbury and Possum Kingdom Reservoir and with recent rainfalls is expected to continue, according to agency officials.

Golden alga blooms occur periodically in slightly salty waters of rivers and reservoirs in west and north central Texas. Portions of the Canadian River, the Pecos River, the Colorado River system and the Brazos River system are currently experiencing impacts from golden alga blooms. An active fish kill in the stilling waters below the dam on Lake Meredith marks the first documented case of golden alga in the Canadian River, according to TPWD.

Investigators with TPWD's Kills and Spills Team report the active bloom in the Brazos River watershed has killed about 5 million fish, mostly threadfin shad, valued at nearly $900,000. By comparison, a 2001 golden alga outbreak on Possum Kingdom Reservoir, Lake Granbury and Lake Whitney resulted in a loss of 600,000 fish valued at $650,000. Additionally, the toxic alga wiped out TPWD's yearly production of striped bass when it got into the Dundee Hatchery's water source.

The species of golden alga that is affecting Texas is Prymnesium parvum. This alga releases a toxin that kills gill-breathing organisms such as fish and clams. According to the Texas Department of Health, anecdotal evidence has shown no human health risks associated with golden alga. Livestock have been observed drinking from rivers during active golden alga blooms without apparent harm.

Golden algal blooms turn the water yellow, gold or a dark tea color. Although no one knows what causes golden alga to bloom, researchers know that conditions that make water salty like drought, brine contamination from oil and gas production, intensive water use and some irrigation practices might contribute to the conditions necessary for blooms.

Following the 2001 outbreak, a committee of scientists led by TPWD developed a set of proposed research projects to address management and potential control options for this alga. Researchers hope to determine, among other issues, how and why golden alga occurs, the potential distribution of the alga in Texas and the ecological and economic impacts from outbreaks.

Thus far, TPWD has funded a project through Texas A&M University designed to determine which nutrients stimulate growth of golden alga and has funded a golden alga culture collection effort to store samples at the University of Texas for future research. TPWD biologists have also researched ways to control golden alga in fish hatchery settings.

Gary Saul, TPWD hatcheries chief, says the toxin has been found in fish hatchery ponds even after the water has been drained. "What we've learned is that even when we drain a pond, there's a resting period where the alga will remain in the mud, and when we add water back, we still have the alga," he said. "We have to determine when and how to treat the ponds to effectively control this organism."

The pond culture industry in Israel has found aggressive treatment with ammonia can reduce a golden alga toxic bloom, allowing restocking of the culture ponds, said Dave Sager, TPWD freshwater conservation branch chief. While the treatment might be effective for farm ponds and hatcheries, it would not be cost-effective or practical for large water bodies. "In addition to the cost and problems with treating such large reservoirs, the concentrations of ammonia required would have adverse impacts on other organisms in the aquatic ecosystems," Sager noted. "The cure could be as bad as the problem."

Harmful algal blooms have been known to occur for hundreds of years. Spanish explorers reported incidents in the Gulf of Mexico when massive fish kills occurred which were probably red tides. Texas experiences three types of harmful algal blooms: red tide, golden alga and blue-green alga.

Red tides in the Gulf of Mexico are caused by a toxic alga called Karenia brevis. Red tide can kill large numbers of fish and cause respiratory irritation for beach goers. Blooms are reddish-brown in color and can actually make large areas of bays or the Gulf appear red. Texas has had six major red tides since 1960. Red tides hurt the economy of coastal communities. During the 2000 red tide, the economic impact to the Galveston area was about $18 million. No one knows what causes red tides.

Red tide is important because the toxin can be concentrated in oysters making them unsafe to eat. The Texas Department of Health closely tracks toxin contamination of oysters to ensure consumers do not get sick from consuming contaminated shellfish.

Blue-green alga, closely related to bacteria, typically form blooms in ponds during late summer. Blue-green alga thrive in nutrient-rich waters and can create a scum layer on the water's surface that looks like someone dumped blue-green paint on the water. Blue-green alga may cause fish kills but also have caused kills of domesticated animals like cattle and dogs that drink the bloom water. High concentrations of blue-green alga cause taste and odor problems in some reservoirs used as drinking water supplies.

top of page

Take Action
  • Report Kills - If you see a fish kill or suspect golden alga, contact TPWD's 24-hour communications centers at 512-389-4848 (Austin).
  • Get the Facts - TPWD has collaborated with the Texas Commission on Environmental Quality and other entities to produce a golden alga information card. Download a PDF from the TCEQ website or request a free hard copy from TPWD at