The largest red tide bloom seen in Florida in nearly a decade has killed thousands of fish in the Gulf of Mexico and may pose a greater health threat if it washes ashore as expected in the next two weeks.

The patchy bloom stretches from the curve of the Panhandle to the central Tampa Bay region. It measures approximately 80 miles (130 km) long by 50 miles (80 km) wide.

Red tide occurs when naturally occurring algae bloom out of control, producing toxins deadly to fish and other marine life. The odorless chemicals can trigger respiratory distress in people, such as coughing and wheezing.

"It could have large impacts if it were to move inshore," said Brandon Basino, a spokesman for the Florida Fish and Wildlife Conservation Commission (FWC). "It has been killing a lot of marine species, especially fish, as it waits offshore."

The agency has received reports of thousands of dead fish, including snapper, grouper, flounder, crabs, bull sharks, eel and octopus. This is the largest bloom seen since 2006.

The phenomenon has existed for centuries, but such a large bloom is being closely monitored in Florida because it could impact beach tourism and commercial fishing.

A smaller red tide bloom, closer to shore, contributed last year to a record number of deaths among Florida manatees, an endangered sea mammal.

REUTERS