More sick and dying fish, some with rotting fins and missing eyes, have been found in Treasure Coast waterways, and researchers are at a loss this time to say why.
Residents have reported seeing fish with lesions and decaying flesh in the north and south forks of the St. Lucie River and in smaller creeks and canals. Unlike the earlier outbreak that involved numerous species, the sickness appears limited to mullet.
Some people are worried that the Treasure Coast will suffer another outbreak of sick and dying fish similar to last winter and spring. That outbreak hurt charter fishing tours, bait shops and other businesses that depend on tourism.
"We've seen some sick fish throughout the entire time, but the numbers were decreasing," said Melissa Meeker, a supervisor with the state Department of Environmental Protection. "Now, it appears to be increasing."
Peter Greico of Port St. Lucie said anglers Wednesday caught six fish with lesions in an hour. One mullet was missing an eye, and another had a rotting tail.
"It's not just an isolated case," Greico said.
Last winter, large discharges of water from a rain-swollen Lake Okeechobee were suspected of causing the fish disease in the St. Lucie and Indian rivers.
The discharges were thought to cause the growth of a toxic micro-algae by altering saltwater levels in the estuary.
There have been no discharges from the lake since June, and rainfall has been minimal in recent weeks. Nevertheless, the DEP's Marine Research Institute in St. Petersburg says the fish kill appears to have returned.
"The problem never went away completely," said Leigh Demateis, an institute spokeswoman. "One or two lesioned fish in an area are normal. Many lesioned fish is not and could indicate something else. The anecdotal evidence is the fish kill problem could be back."
One theory posed by fishing guides and some environmentalists is that polluted runoff has saturated sediment at the bottom of local rivers. The sediment is then churned during windy conditions and the poison infects the fish.
Paul Millar of the South Florida Water Management District says besides the rotting fish, the estuary appears healthy.
"It truly is a mystery," he said. "The estuary is in great shape."