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Golden Alga in Texas

Archived News Release

Oct. 29, 2001

Latest Fish Kill Blamed on Naturally Occurring Golden Algae

SAN ANGELO, Texas — Golden algae, a naturally occurring alga that releases a toxin that has been responsible for fish kills in several Texas river basins earlier this year, has resurfaced, this time on E.V. Spence Reservoir and other nearby impoundments.

The golden alga (Prymnesium parvum) was confirmed earlier this week in connection with fish kills on E.V. Spence Reservoir and on Moss Creek City Lake. The toxin produced by this alga may also be present in Colorado City Lake but with no associated fish kills.

Unlike an extended outbreak earlier this year that caused major fish kills at Possum Kingdom Reservoir and Lake Granbury, the current algal bloom appears to have had nominal effects on the fisheries so far, according to Bobby Farquhar, a San Angelo-based fisheries biologist with Texas Parks and Wildlife.

"We verified that it is golden algae in Spence, and we have been monitoring the situation," Farquhar said. "The kill showed up last week, and we observed dead fish — primarily threadfin shad and freshwater drum — in the thousands throughout the entire lake. We also observed hundreds of dead game fish, including striped bass, but it appears that not a lot of fish are dying at present."

TPW's Kills and Spills Team has been taking water and fish samples in the affected areas daily, and, according to team member Kip Portis, the situation appears to be subsiding. "I was on Spence on Wednesday taking samples and saw no freshly dead fish. I did see some shad, and they did not appear lethargic so maybe we're seeing an end to this," he said.

Golden algae were identified for the first time in Texas during a fish kill on the Pecos River in the 1980s. The brackish water organism is believed to be responsible for fish kills in several Texas river basins, including the Rio Grande, Colorado, Red and Brazos. Although golden alga poses no health risks to humans even in drinking water, it can be lethal to gill-breathing organisms: fish and bivalves. "Prymnesium parvum is not known to be a human health problem," said Kirk Wiles of the Texas Department of Health. "But, as is always the case, people shouldn't pick up dead fish and take them home to eat. That's just common sense."

Recent electro-fishing surveys by TPW indicate that Spence's fishery was in good shape prior to the algal bloom with an abundant supply of forage fish, and based on current loss estimates should not be severely impacted by the kill. "We've had reports of anglers catching live shad in their cast nets this week," Farquhar noted. "We saw a good number of largemouth bass in our surveys, so we were in pretty good shape going into this."

While biologists are assessing the current golden algae situation on Spence and monitoring conditions along the Colorado River, researchers elsewhere in Texas are trying to identify the possible causes and potential management solutions of a toxin producing organism that is showing up in new places.

"This algae has possibly always been in the river systems, but for some reason is now expanding its range," offered David Sager, TPW freshwater conservation branch chief. "We're trying to pull together historical data to find common factors involved in fish kills that might be connected to golden algae. In the affected lakes, we've noted high salinity levels combined with an extended drought which created conditions that gave this algae a competitive edge over native algae."

Other possible contributing factors, he said, include uncapped, abandoned water wells within the watershed, which put more salt in the river system. "Unfortunately, a state program to cap these wells has not been able to take care of all the wells yet," Sager noted. "There's also non-point-source runoff and other discharges into the rivers that could be having an impact. The good news is there are management possibilities out there. They're not cheap, and it's not something you want to jump on until you know it'll have the desired effect."

Researchers also theorize that fish may be learning to adapt to conditions during a golden algal bloom. "Unless you get a massive outbreak like we saw (at Possum Kingdom) this year, fish have shown an ability to move out of harm's way," said Sager. "We've confirmed this on the Pecos River and at Red Bluff, where we've seen the algae historically. Also, you wouldn't expect to get a bloom like this every year, and that allows the fish community to come back."

Joan Glass has been tracking and researching golden algae as part of her role with TPW's Kills and Spills Team and believes the toxic algal species may have been the culprit on earlier fish kills. "The symptoms fish show during golden algae blooms are similar to those that died from low dissolved oxygen levels," she pointed out. "We've got records of fish kills in these areas dating back to the '60s that could have been caused by golden algae, but we didn't have the water chemistry equipment back then to tell us what a bloom was. What we do know is that unlike with some other toxins, fish can survive if removed from the affected areas, and the blooms don't appear to have a long term affect on the resource."

Mark Howell, a TPW fisheries biologist in Wichita Falls, manages Possum Kingdom Reservoir and says he's already seeing signs of recovery there. "The bloom moved all the way down the lake and then all the way back up, so essentially it got hit twice, but there was a pretty fair number of fish that survived and found refuge up in the river," he explained. "From our electro-fishing surveys we completed this week we saw very good numbers of shad that not only survived but appear to have reproduced well. There are also reports of anglers catching good numbers of large catfish in the upper end of the lake."

It appears from early returns that Possum Kingdom will recover, but Howell said it could take a while. "What we didn't find in our surveys were very many largemouth bass older than the young of the year anywhere in the lake. That tells me we lost a good share of that fishery, but we found excellent growth among those bass that we stocked this year."

TPW stocked 450,000 Florida largemouth bass fingerlings in May, and Howell said it will take a couple of years before there will be a substantial bass fishery on Possum Kingdom. "We'll be assessing the crappie fishery in November, and I expect those populations to be depressed as well," he said.

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Aditional Information:

Would you like to know more?
The Biology of Golden Alga summarizes what we know about the alga and its toxins.

Where does golden alga fit compared to other single-celled organisms?
The Golden Alga Family Tree gives examples of and information about golden alga and other protists.

What does golden alga look like?
TPWD Golden Alga Images has photos of fish kills, golden algal cells, and short videos of live golden alga. These images may be used for noncommercial/educational purposes as long as TPWD is given credit and other site policies are followed.

Golden Alga Information Card: 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

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