Key Largo fish kill still a mystery

Scientists still don’t know what killed scores of fish and left a milky white sheen in the water in several Key Largo canals two weeks ago.

Biologists with the Marine Resources Development Foundation conducted water samples of a canal behind Heron Road, off mile marker 95. They found some sort of phytoplankton species, but they're not sure what it is or if it is responsible for killing the fish.

"There are 10 to 15 common types of phytoplankton species," said biologist Sarah Egner. "I'm not positive on the ID."

Mark Hall, the Heron Road resident who first reported the fish kill, is unsettled by the finding.

"The fact that they couldn't identify the species is a little disturbing," Hall said.

The bulk of the fish were killed between Friday, June 26, and Monday, June 29. The phenomenon wasn't isolated to the Heron Road canal. Residents five streets south of Hall's home had similar reports.

Ed Holly, whose family has owned his Bonito Lane home since 1958, said he had never seen the typically gin-clear canal so murky as it was following that weekend's fish kill.

Paul Christian, general manager of the Key Largo Wastewater Treatment District, said there were no reports of sewage line breaks or leaks in the area.

Egner and her colleagues sent the sample they collected to Charleston, S.C., to have it examined by biologists with the National Oceanic and Atmospheric Administration.

Egner said the sample looked similar to the phytoplankton species gambierdiscus. Fish that infect people with the food-borne illness ciguatera have flesh that is infected with gambierdiscus.

Many other things could have killed the fish, however, including the water temperatures that have risen quickly over the past few weeks. This can cause plants on the ocean floor to suck the oxygen out of a given area, which makes it harder for fish to breathe.

Sargasso weed masses, common this time of year, can also choke the oxygen out of the water.

Hall hopes an answer comes quickly.

"I'm just nervous about swimming in the canal," he said. "My grandson swims in there also. It's a little unnerving."