OLDSMAR — An algae bloom of unknown origin has killed what a Pinellas County official described Thursday as "thousands and thousands" of fish in an outfall canal between Lake Tarpon and the northern reaches of Tampa Bay.
The algae bloom near Oldsmar appears to have absorbed much of the oxygen in the water in that area, suffocating thousands of juveniles of a type of fish known as menhaden.
"The menhaden are the only ones that have been affected," said Kelli Hammer Levy, director of the county's environmental management division.
The first calls to the state's fish kill hotline came in over the Fourth of July weekend. When officials from the county and the state Fish and Wildlife Conservation Commission checked it out Tuesday, they found the water in the canal near Curlew Road was very low in oxygen.
The bloom and fish kill occurred near the Gull Aire Village mobile home park on Curlew Road. No one at the park's homeowners association responded to a request for comment.
The algae found in the canal is not the same as the toxic algae bloom now plaguing the state's Atlantic coast, Levy said. That algae bloom has so far not caused a fish kill, although its putrid smell has driven tourists away and residents indoors.
Instead, the samples taken from the outfall canal turned up two types of algae: heterosigma, which has caused fish kills in Louisiana, Japan and Brazil; and gymnodinium, which is associated with Red Tide and has been found for more than 100 years in Florida coastal waters from Pensacola to the Dry Tortugas. Both are found in salty or brackish water, not freshwater.
Algae blooms and fish kills are rare in the freshwater of Lake Tarpon, but not unknown. In the summer of 1987, Lake Tarpon suffered a major bloom of a type of blue-green algae that covered 80 percent of the lake. The bloom persisted all summer, but there were only minor fish kills.
No one knows what causes a handful of microscopic algae to suddenly erupt in a bloom of millions of the plantlike creatures that coats the water. Usually it occurs when the water is extremely warm — as it is now — and in areas where nutrient pollution provides a type of fertilizer for rapid growth.
Menhaden spawn in the saltwater offshore, but then the young move into estuarine nursery areas such as Tampa Bay, where they spend the early part of their lives in brackish water. That's likely where the thousands of dead fish in the canal came from.
The county has no plans to go out and scoop up all the dead fish, so anyone who lives nearby has to put up with the smell for a while.
"We do not clean them up," Levy said. "They make fine eating for some birds."
Times senior news researcher Caryn Baird contributed to this report. Contact Craig Pittman at firstname.lastname@example.org. Follow @craigtimes.