GALVESTON - State officials confirmed Monday that a toxic algal bloom known as red tide is responsible for thousands of dead fish that washed ashore on Galveston Island the day before.

Texas Parks and Wildlife Department biologists found the algae Karenia brevis, one of several types of toxic algae that cause red tide, in concentrations high enough to kill fish in samples taken at Surfside Beach and Galveston Island, said Winston Denton, a biologist with the agency's marine fisheries division and a member of its "spills and kills" team.

Biologists are continuing to gather information to determine the extent of the red tide and its concentration, but they can't say yet whether further fish kills will occur or how long the algal bloom will last, Denton said.

A red tide last year covered most of the Texas Gulf Coast and Galveston Bay, forcing a closure of the oyster beds to harvesting, Denton said.

The red tide of low-to-moderate concentrations last year arrived in August and lasted until February but caused no fish kills, he said.

The Texas State Health Services Department's seafood safety division halted oyster harvesting in Galveston Bay because of red tide at 12:01 a.m. Monday, Health Department spokesman Chris Van Deusen said. Van Deusen said the economic impact would be relatively light because harvesting by the oyster industry and the public is at a low point this time of year.

Parks and Wildlife said reports of hundreds of dead fish came on Saturday, but on Sunday dead fish littered the beach by the thousands. Dead flounder and stingrays were reported Friday in Kemah and Bacliff, but Denton said more testing remains to determine whether the deaths were caused by red tide or low oxygen levels in the water.

Reports of dead fish came from Quintana Beach in Brazoria County to the mouth of the Colorado River, the department said on its web site.

Most of the dead fish were menhaden, Denton said, which are more susceptible than other species to red tide. The fish are common and swim in large schools, he said.

In Galveston, Parks Board Executive Director Kelly de Schaun said crews worked overnight to clean the beaches most frequented by the public and the western end of the island, which had the largest concentrations of dead fish. A second, smaller wave of dead fish arrived Monday morning and was removed, she said.

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Red tide being blamed for fish kill at Galveston beaches