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Golden Alga in Texas

Archived News Release

Feruary 9, 2001

Update on Possum Kingdom and Granbury Fish Kills

AUSTIN, Texas — Texas Parks and Wildlife biologists continue to monitor and investigate recent fish kills on Possum Kingdom and Lake Granbury, and staff are asking the public to help by reporting any new movement between Lake Granbury and the Lake Whitney area.

Prymnesium parvum, a bio-toxic golden alga, has been confirmed as the cause of both fish kills. Prymnesium parvum is a microscopic plant that exists in small quantities year-round throughout the Brazos River watershed where water conditions allow it to survive, according to TPW. Large concentrations, or blooms, cause water discoloration ranging from yellow to coppery-brown and are toxic to fish.

"At this point, the large blooms are limited to Possum Kingdom and Granbury," said Jack Ralph, TPW program leader for the Inland Kills and Spills Team. "But, there is the potential for the blooms to continue downstream in the river or possibly into Lake Whitney. We need folks familiar with the area to help us by reporting any new impacted areas or dead fish."

Residents who observe yellow discolored water, concentrations of dead fish, or foaming on the Brazos River or Lake Whitney are encouraged to contact Texas Parks and Wildlife resource protection staff or the Brazos River Authority.

On Possum Kingdom the growth of blooms has slowed, while Granbury is now close to 80 percent impacted with spotty blooms, according to TPW biologists. TPW Kills and Spills Team members were on-site at Possum Kingdom Wednesday and report that the blooms are increasing at approximately one to two-miles a week, a much slower rate than what has been observed in the last two weeks.

Counts conducted last week at Possum Kingdom estimate 175,000 dead fish and counts conducted this week at Lake Granbury estimate 261,000 dead fish.

On both reservoirs, forage species such as freshwater drum and gizzard shad comprise the majority of the fish killed. Game fish have also been affected. While lethal to gill-breathing organisms, fish and bi-valves, the algal toxin is not known to harm other species or humans.

"Prymnedium 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."

To report new movement of the Prymnesum parvum blooms in the Brazos River or Lake Whitney area, call TPW at (512) 389-4848 or (512) 912-7153; or the Brazos River Authority at (254) 776-1441, ext. 241., or e-mail

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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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