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SOLVED: Fish die-off caused by toxic alga bloom

Hundreds of dead fish popped up at Conquistador Lake last week, causing concern among many visitors.
Kaysie Ellingson
Hundreds of dead fish popped up at Conquistador Lake last week, causing concern among many visitors.

Shisbeth Tabora collected water samples from Conquistador Lake near the Buddy Holly Recreation area in Northeast Lubbock. She is a graduate student at Texas Tech’s department of Natural Resource Management and frequents the Canyon Lake system to monitor the conditions as part of her research. But this day was different. On this day she was trying to solve a mystery.

As she dipped her plastic container into the water, dead fish bobbed around her arm—that was the unusual part.
 

Shisbeth Tabora collects samples of water from the Canyon Lakes in search for an answer to what killed all the fish.
Credit Kaysie Ellingson
Shisbeth Tabora collects samples of water from the Canyon Lakes in search for an answer to what killed all the fish.

“I didn’t expect to see this in Lubbock,” she said as she made her way to her second collection site at the base of the dam. This was her first time working with a fish die-off in the city.

If you visited the Buddy Holly Recreation area last week, you probably noticed it—the hundreds of fish carcasses drifting across the lake. If you got close enough you could catch the scent of decaying Carp and Catfish—the resilient fish of the bunch. But apparently not enough to withstand whatever happened here.

“To find [Carp and Catfish] among the dead fish, that means whatever it was it was strong,” Dr. Reynaldo Patino said. “The lethality was high to be able to kill fish like common Carp.”

Patino is Tabora’s research professor and a U.S. Geological Service Senior Scientist. He’s been monitoring the lakes with his students since 2003—recording temperature and oxygen levels, as well as specimen counts like alga density. He’s seen a few fish die-offs in his time in Lubbock, but since this one was in a well-trafficked place, it got a lot of attention.

While most often these occurrences are triggered by natural causes, Patino said it damages the aesthetics of a place. “Who wants to come here and fish or do other activities around the water when there’s a lot of dead fish around?”

Both Patino and the city of Lubbock fielded several phone calls from concerned citizens. Many believed pollution from the surrounding industrial areas was the culprit as photos circulated around social media hundreds of dead and decaying fish floating on the lake's surface. When Ronny Gallagher, with the Parks and Recreation Department, caught word of the severity of the event, he went to see it for himself.

“There were several dead fish,” he recalled, “and some were in the process of dying.” Since the water in this lake system is reclaimed water, he reported his finding to the water department. He wanted to be sure the treated water wasn’t harming the aquatic life. “I called them to let them know so that way if there was any question, they would be able to look at it.”

They reported it to Texas Parks and Wildlife as well as the Texas Commission on Environmental Quality—both agreed with the department’s conclusion that a temperature drop the week prior resulted in the deaths.

Patino said, “Normally when we see temperature shocks, we’re talking five degrees Celsius, maybe not that low…but it has to be a huge temperature drop.”

According to Tabino’s records, the temperature of the water was 18 degrees Celsius the morning temperatures dropped. More importantly, that day she already noted dead fish—so based on those observations, it couldn’t have been caused by the temperature.

“The first time I heard about the dead fish was Shisbeth. She sent me an email and said, 'Hey there were dead fish.' that was last week,” Patino said. While the group worked to collect samples at the dam, they noticed a slow-moving, black carp slithering around the murky waters.

Patino walked closer to the water’s edge. It barely moved. “Carp would not let me get this close if it was normal.” A lethargic fish is another piece of evidence indicating that whatever was affecting them wasn’t fully gone. “My hunch is this is due to Golden alga,” Patino said. “Harmful alga.”

Turns out, Patino’s hunch was correct. After sending the samples they collected to Texas Parks and Wildlife Department, a DNA test confirmed that a toxic bloom of Golden alga killed the fish. It’s not the first time they’ve seen this alga here.

Last fall, in this same spot, the team observed a massive Golden alga bloom. Normal levels of Golden alga have a density of under 10 thousand cells per milliliter. Last fall, they counted around 100 thousand. In that case, it wasn’t toxic. This year, while it’s not as dense, it clearly is toxic.

The good news for visitors to the lake is that Golden alga is only known to be toxic to animals with gills, like fish and frogs—so you and your dogs are safe.

But there’s still a lot they don’t know about it. “The million-dollar question is how can we predict it,” Patino said. Over 17 years, they’ve seen seven or eight toxic blooms—but they don’t know why they happen on some years and not others.

The answer to that question could help mitigate future fish die-offs, and may shed light on what is happening in Lubbock’s aquatic ecosystems.

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