The Texas Parks and Wildlife Department is reporting red tide along the lower Laguna Madre.

High to moderate concentrations of red tide have been found from Beach Access 6 to the Brazos Santiago jetties. Moderate cell concentrations have been found at the Isla Blanca Park boat ramp.

Red tide — what scientists call “harmful algal blooms” — occurrs when algae grows out of control, according to the National Oceanic and Atmospheric Administration. The algae produces toxins that kill fish and irritate the human respiratory system.

The blooms also turn the water red.

Beachgoers have been experiencing eye irritation and itchy throats as a result of the red tide.

“We just got here and didn’t expect this. We just started looking and saw fish everywhere, dead,” said Mary Chapel, who visited the beach Wednesday.

To monitor the presence of the red tide algae, officials have been taking water samples every day.

“When the wind blows it on shore, people breathe it and it irritates our respiratory system,” said Tony Reisinger, a marine specialist with the Texas Sea Grant College Program at Texas A&M University.

Reisinger said said calm winds are helping conditions stay mild on the island, but he advises people with respiratory problems to stay off the beach.

Dead fish found on the shore and shellfish should not be consumed.

“They accumulate the toxin so you can get sick from eating them,” Reisinger said.

Red tide could last anywhere from a few weeks to months.

In 2015, an outbreak of red tide lasted about three months on South Padre Island.