Environmentalists, including those at the Sanibel Captiva Conservation Foundation, are keeping a close watch on an abundance of unusually dark water that has moved in along the islands' beaches and in the Caloosahatchee River estuary in recent weeks.
Excessive rainfall in the Lake Okeechobee and Caloosahatchee River watersheds over the past two months is causing the discoloration due to freshwater releases from Lake Okeechobee by the U.S. Army Corps of Engineers and South Florida Water Management District. Releases into the Caloosahatchee wind up reaching the Gulf of Mexico at Sanibel.
The normally clear green or blue beach waters turn a dark tea color because it contains tannins from organic and plant material it picks up along the way.
A Sanibel Captiva Conservation Foundation Marine Laboratory boat heads for the trailer last week in the dark, tea-stained water that has reached the Tarpon Bay Explorers’ launch area at the J.N. “Ding” Darling National Wildlife Refuge on Sanibel.
According to the SCCF website, as of July 23, the salinity level at Iona is in the "lethal" range for shoal grass and oysters.
"High oyster mortality at Iona is expected," the website report states. Chlorophyll spikes have been measured at Tarpon Bay and Redfish Pass.
"Beaches along Fort Myers Beach continue to experience patchy stranding of red drift algae," according to SCCF monitors. "Dead sea grass has been observed along the beach. Water color is highly stained and dark along the beach as the river plume stretches along the island and into Matanzas Pass."
According to a report from the Lee County Health Department, it is safe to swim in the stained water as water quality samples are taken and tested weekly with the results posted on its website www.leechd.com.
The discoloration is expected to dissipate when the heavy rain and freshwater discharges are halted.