The seabirds began dying soon after the sewage began flowing.
The culprit may be some very nasty bacteria in the water.
In all, 48 fledgling black skimmers died in September after two Pinellas County cities dumped sewage into Boca Ciega Bay, according to Elizabeth Forys, an Eckerd College professor studying the birds.
Official laboratory tests on the cause of those deaths are still under way, but one of the birds was confirmed to have died of salmonella, she said. The salmonella appears to have resulted from bacteria found in the water after St. Petersburg and Gulfport dumped sewage in the bay, she said.
Lab tests on water samples taken by Forys found levels of bacteria 100 to 1,000 times above normal, she said.
The amount of bacteria wasn't the most worrisome part of the discovery.
"The type of bacteria found was very unusual — Escherichia fergusonii," Forys said. "This is a highly pathogenic bacteria that has caused death in birds and mammals (including humans) and is largely antibiotic resistant."
A University of South Florida researcher found a different strain of antibiotic-resistant bacteria in waters along St. Petersburg's shoreline after the city dumped millions of gallons of sewage into Tampa Bay.
Heavy rains in August prompted a number of Pinellas County cities to dump sewage into area waterways. Gulfport dumped 302,400 gallons into Boca Ciega Bay on Aug. 8.
Hurricane Hermine exacerbated the problem when its rains lashed the Florida peninsula in September. Gulfport officials estimated an additional 892,500 gallons spilled Sept. 2, the day the storm made landfall in North Florida
Meanwhile, St. Petersburg's overwhelmed sewer system dumped more than 200 million gallons of waste into waterways, roadways and neighborhoods over about 15 months. Most went into Tampa Bay.
Researcher Suzanne Young tested water samples from near the shoreline along Lassing Park and Harborage Marina. She found vancomycin-resistant enterococci, a strain of dangerous bacteria not usually seen outside hospital waste. She and a colleague found that same genus in Joe's Creek in Pinellas after a 2014 sewage spill there.
However, she said, the possibility that this type of bacteria came from the sewage spills remains unproven.
"It's hard to make the connection," she said.
Skimmers are easily identified by their vivid red-and-black bills. A flying skimmer drags its knife-thin bill through the water, scooping up small fish to eat, then snapping its bill shut. One 1930s biologist compared them to "aerial beagles hot on the scent of aerial rabbits."
Black skimmers are currently classified as a species of special concern in Florida, but state officials are leaning toward raising that level of protection to threatened, according to Forys.
Because they're an imperiled species, and Pinellas County supports about 30 percent of the 2,000 breeding pairs of skimmers that remain in Florida, volunteers from the Florida Shorebird Alliance were going out daily in August to monitor their nesting.
That's how they found the dead birds.
Forys watched one die. She said she saw it "dragging its wings, then looked to have convulsions and flipped onto its back."
Contact Craig Pittman at [email protected] Follow @craigtimes.