ST. PETERSBURG — Pelicans are dying around Riviera Bay and Coffee Pot Bayou and so far no one knows why.

"It's awful, it is," said Eddie Gayton of the Seaside Seabird Sanctuary.

Dead birds have been turning up since Wednesday. The sanctuary is caring for 14 pelicans that are still alive but lethargic and paralyzed, he said. They appear to have been poisoned by something, but by what is the mystery. Another 22 died, he said, along with an egret that may or may not be part of the pelican die-off.

And other wildlife rehabilitation facilities have taken in sick pelicans as well, said Barbara Walker of the Clearwater Audubon Society.

"Nobody has a total," she said. "We don't have a good protocol here (for dealing with sick birds). And these birds are all being treated different at different facilities."

There are no lack of suspects. The wave of sickness and death may be connected to an ongoing Red Tide algae bloom, although some bird advocates fear what's going on could be linked to the city's massive dump of sewage into Tampa Bay during last year's storms.

However, the brackish Riviera Bay doesn't directly connect to Tampa Bay, with Weedon Island lying in between. As a result, Gayton questions the theory of sewage dumping being the culprit. Walker said the birds could have picked up their illness elsewhere and then flown to Riviera Bay.

Florida Fish and Wildlife Conservation Commission biologists and St. Petersburg crews have taken water samples as part of an investigation of the die-off. The biologists have also sent three dead pelicans to a laboratory to determine what killed them, said Michelle Kerr of the state's Fish and Wildlife Research Institute in St. Petersburg. She said results might be available in two weeks.

In the meantime, the sanctuary is treating the sick birds with fluids and a charcoal solution that helps remove toxins, Gayton said.

For the ones that are paralyzed, "We're keeping their heads propped up so they don't sustain an eye injury," he said. A pelican with a damaged eye cannot fly or catch fish.

Gayton said the sanctuary received its first call about dead birds on Wednesday from Riviera Bay, a subdivision near Weedon Island. He said the lake regularly suffers from a thermal inversion condition that kills thousands of fish, but longtime residents told him it's the first time they've seen birds die too.

"My hope is that the pelicans found in Coffee Pot Bayou got sick at Riviera Bay and then swam or flew over there and died," Gayton said. If not, then something in the bayou may be sickening the birds too.

The survivors are showing symptoms that could match a diagnosis of poisoning by Red Tide, he said. Red Tide has stunk up Florida's beaches for centuries. Spanish explorers recorded blooms when they visited in the 1500s.

Small, scattered colonies of the microscopic algae Karenia brevis — named for retired St. Petersburg biologist Karen Steidinger, who spent decades studying it — live in the Gulf of Mexico all year long. Usually they cause no problems.

But every now and then, the algae population offshore explodes into something called a bloom in which the algae multiplies rapidly and spreads. The expanding bloom stains the water a rusty color that gives the creature its name.

No one knows what causes the bloom to begin offshore, and no one knows what causes it to end.

The big blooms release toxins that are deadly to marine creatures. A bloom along the Southwest Florida coast in 2013 killed 200 manatees.

Those blooms can last for months, fueled sometimes by nitrate pollution flowing from overfertilized yards, leaky septic tanks and other sources, including the sewage dumped by cities.

Last year Hurricane Hermine, along with earlier summer storms, overwhelmed the sewage treatment plants in St. Petersburg, Gulfport and other Pinellas cities, leading them to dump tens of millions of gallons of sewage into both the Tampa Bay and Boca Ciega Bay. Just this weekend, St. Petersburg Mayor Rick Kriseman contended that the sewage did not harm the environment.

So far, the die-off hasn't approached the level of the one that plagued the Indian River Lagoon on the state's Atlantic coast between 2012 and 2013. During that time, more than 300 pelicans died, along with dozens of dolphins and more than 150 manatees. Scientists have yet to figure out what killed them — and the manatee die-off began again last year.

Times staff writer Charlie Frago contributed to this report. Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes.