The good news: Lake Okeechobee has finally stopped rising.
The bad news: The lake is nearly a foot higher than the top of its ecological envelope.
The heavy rainfall from Hurricanes Ian left about 1 million acre feet of water north of the lake. After Hurricane Ian, to relieve flooding in the Orlando/Kissimmee area, water managers pumped water down the Kissimmee Chain of Lakes into the Kissimmee River and let it flow rapidly south into Lake O, causing the lake level to rapidly rise. In a matter of weeks, the lake level rose about 3 feet.
Nature did not design the lake to rise so quickly. According to the U.S. Geological Survey, before the flood control dredging and ditching that made it possible for millions of people to live in South Florida, rainfall that fell at the top of the system in the Orlando/Kissimmee area took about six months to slowly sheetfall south into Lake Okeechobee. Along the way, much of that runoff evaporated into the air or percolated into the earth, recharging the aquifer. The water that did make it to the lake had been cleaned by vegetation along the way.
According to the Dec. 14 Ecological Conditions Report from the South Florida Water Management District, most lakes in the Kissimmee Chain of Lake are now at regulation schedule, although releases continue to be made for local basin runoff. Water depth on the Kissimmee River floodplain has decreased from the previous week. Oxygen levels in the river have increased.
The ecological envelope – the healthy range for Lake Okeechobee – varies from 12 ft to 12.5 feet (above sea level) at the beginning of the wet season to 15.5 feet at the end of the wet season. At 15.5 feet, the marshes which surround the lake are completely inundated with water. As the lake level rises, water stacks up against the side of the Herbert Hoover Dike, the earthen berm that encircles the lake for flood control. Water levels above 15.5 feet can damage or destroy the marshes and the submerged aquatic vegetation (SAV) which not only clean the water but also provide habitat for fish and wildlife.
According to the report, this is the third year in a row the big lake has started the dry season above 16 feet. The lake is at its highest level for this time of year in more than two decades.
No water from Lake Okeechobee has been released east to the St. Lucie River since April 2021. The Lake Okeechobee Regulation Schedule (LORS) calls for releases of 1,800 cubic feet per second under current conditions. However, the U.S. Army Corps of Engineers opted not to make any releases to the St. Lucie River.
LORS also calls for releases of 4,000 cfs to the Caloosahatchee River under current conditions. The U.S. Army Corps of Engineers has set the target flow to the Caloosahatchee at 2,000 cfs, measured at the Franklin Lock. The Franklin Lock is more than 40 miles from the Julian Keen Jr. Lock at Moore Haven, where lake water enters the river. Flow at the Franklin Lock is a mixture of lake releases and local basin runoff. For the week of Dec. 5-11, about half the flow to the Caloosahatchee came from the lake.
During the dry season, the Caloosahatchee River needs freshwater flow from Lake O to keep the salinity levels in the estuary in the optimal range. If the freshwater flow at the Franklin Lock falls below 457 cfs, the salinity levels rise too high. If the flow at the Franklin Lock exceeds 2,600 cfs, the salinity levels can drop too low. Optimal sality levels vary for different parts of the estuary. According to the Dec. 14 SFWMD Ecological Report, with the flow at 2,000 cfs, salinity in the upper Caloosahatchee estuary was in the optimal range for tape grass. Salinity levels at Cape Coral and Shell Point were in the optimal range for oysters.
South of Lake Okeechobee, the water levels have receded in the stormwater treatment areas (STAs), allowing more water from the lake to move south. For the week of Dec. 5-11, about 11,870 acre feet of water from the lake flowed south. (An acre foot is the volume of water required to flood one acre of land one foot deep.) About 14,400 acre feet of water flowed west to the Caloosahatchee. Most of the water leaving the lake – 28,860 acre feet – was through evapotranspiration (a combination of evaporation and plant transpiration). Flow into Lake Okeechobee from the north – primarily from the Kissimmee River – totalled 33,250 acre feet. The report indicated there was no direct rainfall into the lake for the week.