High water levels are hurting Lake Okeechobee’s ecological balance.
Water Resources Director Terrie Bates explained the issue at the July 12 meeting of the South Florida Water Management District Governing Board.
She said it is due to the lasting effects of Hurricane Irma, which churned the waters of the Big O and dumped enough rain to push the lake level up to 17.2 feet as the watershed to the north drained into the lake.
Because of that churning by Hurricane Irma’s winds, turbidity levels and dissolved nutrient levels in the water remained high. In the dry season, the lake slowly dropped to 12.8 feet, but then it was quickly pushed back up by the heavy rainfall in May. The wet-season rains came too soon.
Phosphorus levels, although they have come down, are still significantly higher than they normally are at this time of the year, she said.
The lake has really been hampered three years in a row by very high stages, Ms. Bates explained.
The loss of aquatic habitat, both from the storm surge that ripped vegetation out of the lake and from the high water levels, means there are fewer plants in the water column to uptake the phosphorus. The aquatic vegetation also provides critical habitat for fish and wildlife.
“The lake is certainly hurting,” she said.
In 2009, the lake had about 46,000 acres of submerged vegetation. In 2015, Lake O had 33,345 acres of submerged vegetation, she said. After Hurricane Irma, it had 11,609 acres.
Because the dry season did not drop the lake low enough for a long enough time period, the vegetation around the lake’s edges did not have a chance to recover, Ms. Bates said.
South of the lake, the Stormwater Treatment Areas (STAs) also took a blow from Hurricane Irma. The STAs processed a record 1.6 million acre-feet of water last year, she said.
In the Everglades, the tree islands are also suffering from high water levels for the third year in a row.
The damage to the marshes from the high lake levels means the lake’s water is higher in phosphorus and nitrogen due to the loss of vegetation that would clean the water, Paul Gray, of Florida Audubon, explained at the July 31 meeting of the Okeechobee Rotary Club.
The loss of the plant communities means loss of habitat for fish and wildlife, he said.
Dr. Gray explained that the flood control system was designed in the 1940s. Even then, officials knew it had to be a balancing act between flood control and water storage, he said. If you overuse the flood control system, you will have water shortages, he said.
The system needs to be fixed to prevent the extreme high lake levels, which result in harmful releases to the estuaries east and west, and the extreme lows, which mean water shortages for farmers and urban areas. The way to fix this is with water storage north, south, east and west of Lake Okeechobee, he said.
In the 1970s, the phosphorus level in Lake Okeechobee was about 40 parts per billion, he said. Water entering the lake is many times that level in phosphorus.
The goal is to get it back to 40 ppb.
Dr. Gray said it would be possible to clean up the lake if authorities could control the flow into it. During drought years, he said, when there is not so much water going into the lake, the phosphorus level in the lake water drops.
“When you have drought years and you don’t have the flow of nutrients into the lake, the lake got better,” he said.
While some researchers thought the mud at the bottom of the lake would keep the nutrient level high, this did not turn out to be the case, he said. “This tells us we can clean up the lake if we clean up the watershed.”
Storing water north of the lake can make it possible to clean the water before it goes into the lake, Dr. Gray continued.
Lake Okeechobee anglers have expressed concern that the state’s aquatic plant management program could be harming aquatic vegetation that would be beneficial to the lake.
They are also concerned about the chemical spraying of vegetation on the Kissimmee River, which flows into Lake Okeechobee.
The Florida Fish and Wildlife Conservation Commission’s contractors spray chemical herbicides, which, according to the FWC, target only the invasive species.
According to the Florida wildlife system Invasive Plant Management website, in 2016-17, Florida spent $23,624,861 to control invasive plants on 80,417 acres. On Lake Okeechobee alone, in fiscal year 2016-17, $2,454,320 was spent to spray 17,424 acres, including 13,731 acres of floating vegetation, 26.3 acres of hydrilla and 3,676.6 of other vegetation.