The first call came from an area game warden March 16, and by March 20 TPWD Pollution Biologist Stephen Twidwell was on the river.

“I observed a large number of dead fish,” Twidwell said. “Primarily carp, gizzard shad, channel catfish and Gulf killifish.”

Twidwell said that water samples showed extremely high levels (more than 100,000 cells per milliliter) of golden alga (Prymnesium parvum), an organism that can be toxic to fish and shellfish. While the exact relationship between the amount of golden alga in the water and toxicity has not yet been determined, cell counts as low as 20,000 cells per milliliter can cause fish kills.

Twidwell said that high concentrations of golden alga in Red Bluff Reservoir over the past several months has resulted in fish kills on both the New Mexico and Texas sides of the reservoir and it’s possible that releases into the river sent a slug of toxic water downstream.

“It’s really unpredictable, but I don’t see any reason why it wouldn’t push on downstream,” Twidwell said.

When golden alga gains a competitive edge over other species and blooms (a bloom is an explosive increase in the population of a species), it may produce toxins that result in fish kills. Several toxins may be released that affect gill-breathing organisms, mainly clams and fish but also crayfish and the gill-breathing stage of amphibians.

Unlike toxic red tide blooms on the coast, golden alga toxins have no apparent lethal effect on other organisms besides fish and aquatic creatures. Cattle and other animals have been observed drinking from rivers during ongoing golden alga fish kills with no apparent effects.

Texas Department of State Health Services officials have stated that the golden alga is not known to be a human health problem, but people should never pick up dead, or dying, fish for consumption.

What makes golden alga go into reproductive overdrive and “bloom,” and what can be done to stop it, is not yet known but is the subject of extensive ongoing research by TPWD, university scientists and others.

Monitoring of the current bloom on the Pecos River by the Texas Commission on Environmental Quality and TPWD biologists and game wardens is ongoing.

Members of the public are encouraged to report fish kills by calling the local game warden directly or through the sheriff’s office, the TPWD 24-hour communications center (512-389-4848) or one of the Kills and Spills Team biologists.