WEST PALM BEACH –  Lake releases to coastal estuaries may be slowing soon, but Mother Nature could bring the Big O lake level down anyway.

At the March 13 meeting of the South Florida Water Management District Governing Board, Chief District Engineer John Mitnik  said forecasts for the rest of March and the month of April predict below average rainfall.

He said there is a 50% probability Lake Okeechobee will be 11.5 feet by June 1.

In December, the U.S. Army Corps of Engineers increased lake releases to the Caloosahatchee River and began releases to the St. Lucie in an effort to help lower the lake level before June 1, to allow the lake’s submerged aquatic vegetation (SAV) to recover. The SAV has been decimated by back-to-back years of high water levels, which prevented sunlight from reaching the lake bottom.

Lake O needs 90 days below 12 feet or 60 days below 11 feet in order for the SAV to recover.

The lake release schedule set by USACE is in the “non-harmful” range for the estuaries. The target to the Caloosahatchee was set at 2,100 cubic feet per second (cfs), measured at the Franklin Lock, more than 40 miles from Moore Haven, where lake water enters the river. The previous release target was 2,000 cfs. The target includes local basin runoff combined with lake water. The Caloosahatchee River needs some freshwater flow from the lake during the dry season to prevent saltwater intrusion.

The release target to the St. Lucie Estuary was set at up to 1,400 cfs, measured at the St. Lucie Lock, more than 20 miles from Port Mayaca, where lake water enters the St. Lucie Canal (C-44 canal). The target includes a combination of local basin runoff and lake water.

Mitnik said while salinity levels in the coastal estuaries are currently good for adult oysters, oyster spat need higher salinity levels and this may require reducing lake releases.

“It’s something we are closely watching,” he said. “We’re watching for conditions of oyster spat initiating.”

Director of Water Resources Lawrence Glenn said there is a lot more water leaving Lake O than coming in. Evapotranspiration – a combination of evaporation and plant transpiration – is helping to lower the lake.

“Where this is going is looking extremely beneficial for recovery of SAV,” he explained.

“Mother Nature has come through to bring the lake down,” Glenn said.

“Wading bird use is going pretty well because of that lower lake level,” he added.

Most of the water flowing to the St. Lucie is coming from the local basin runoff, Glenn explained, Of the 1,300 cfs flow the St. Lucie averaged the previous week, less than half (about 520 cfs) came from Lake O.

He said they are seeing good growth of SAV in the estuary. Oyster spat season will start soon. “It’s probably about time to start ramping down releases to the St. Lucie,” he added.

“Going to Caloosahatchee side, we have a really good salinity gradient set up,” Glenn continued. He said the salinity levels are at the optimal range. “We don’t want salinity to go too high because that’s when marine predators come in and eat all the spat,” he added.

 South of the lake, water is moving out of the lake for water supply for urban use, agriculture and the environment.

He said there’s a lot of lake water moving through the stormwater treatment areas (STAs) in the Everglades Agricultural Area (EAA) – the second highest total since 1995 in the dry season for moving water south from Lake O into the STAs.

How much difference will stopping lake flow to the St. Lucie make? For the seven-day period ending March 13, flow from Lake O to the St. Lucie averaged 520 cfs. That’s about 336 million gallons per day. For the remaining time until June 1 – about 10 weeks – that’s about 23 billion gallons of water. One inch on lake Okeechobee is about 12 billion gallons.