TALLAHASSEE, Fla. (AP) — Red tide is back in the waters off of Florida’s southwest coast, making birds sick and killing fish, according to a state environmental agency update on Wednesday.

While satellite imagery isn't picking up the toxic algal blooms, the Florida Fish and Wildlife Conservation Commission said it's been detected in the waters between Sanibel Island and Marco Island.

Officials said recent tests that were done on sea birds alerted officials about the bloom.

“Our first indication of this particular event was we had over a dozen cormorants that came into a wildlife rehab center on Sanibel and we tested blood from those cormorants and all of them tested positive for the red tide toxin,” Gil McRae, director of the agency's Fish and Wildlife Research Institute, told commission members during a virtual meeting.

McRae said it was a late season bloom, and that winter weather could likely break it up, but in the meantime the state, local governments and volunteers are trying to identify what areas are being affected.

“We are ramping up every available resource to respond to this red tide,” McRae said. “As of right now it doesn't appear to be nearly as large scale as the ones we've seen in the recent past.”

The toxic bloom overran Florida’s southern Gulf Coast in 2018, killing huge numbers of fish along with scores of sea turtles and the state’s beloved manatees. The bloom also causes respiratory irritations in people which, coupled with the stench of rotting marine life, sent many tourists fleeing beaches, seaside attractions and nearby restaurants.

Red tide is caused by an organism called Karenia brevis, which occurs naturally in the waters off Florida. In an average year, a red tide may bloom in the fall and run its course through the winter months.