Roy Hamon, 13, communicates with his fishing partner, Chavo Reid (not pictured), as they look for bait while fishing the Caloosahatchee River at Royal Palm Park on Tuesday. / Jack Hardman/The News-Press
Caloosahatchee River watchers are waiting to see how freshwater releases from Lake Okeechobee will affect the river and its estuary.
On Monday, the Army Corps of Engineers started a seven-day release with an average flow of 2,500 cubic feet of water per second (67.32 million gallons per hour, or enough water to fill about 100 Olympic-size swimming pools), measured at the W.P. Franklin Lock, also known as S-79.
“It all depends on what happens in the (Caloosahatchee) basin,” said Eric Milbrandt, director of the Sanibel-Captiva Conservation Foundation Marine Laboratory. “If we get a lot of basin rainfall, we could see harm to organisms in the river and lower part of the estuary.”
Water managers like to keep Lake Okeechobee water levels between 12.5 and 15.5 feet to protect the Herbert Hoover Dike, which encircles the lake.
When the lake begins to fill up after heavy rains, the Army Corps releases water down the Caloosahatchee — lake levels were 13.92 feet Monday. Officials also started a seven-day release to the east coast with an average flow of 950 cubic feet of water per second, measured at the St. Lucie Lock near Stuart.
But increasing fresh water in the river can have adverse environmental effects.
“The threshold for harm is 2,800 cubic feet per second at S-79,” Milbrandt said. “If we get a lot of rain, we could get over that threshold and see seagrass losses.”
Turtle grass and manatee grass, which provide essential habitat for many saltwater species, prefer 28 to 35 parts per thousand salinity.
Salinities in the lower estuary are about 30 parts per thousand, but additional fresh water could lower salinities below the sea grasses’ tolerance.
Tape grass, on the other hand, is essential habitat for freshwater species in the upper Caloosahatchee and prefers low salinities — it stops growing when the salinity reaches 10 parts per thousand and dies during extended periods at 15 ppt.
The salinity at Fort Myers is less than 1 part per thousand.
So releases from the lake won’t harm tape grass from the salinity standpoint, but water from the lake is often dark and can prevent sunlight from reaching grass in deeper parts of the river.
Oysters are an important part of the lower river’s ecosystem because a single oyster can filter 10 gallons of water per hour, and hundreds of fish and invertebrate species depend on oyster reefs for shelter and food.
The salinity in the lower river is within the oyster’s preferred range of 14 to 28 parts per thousand (oysters can die if salinity drops below 5 ppt).
“Right now, oysters are doing well,” said oyster expert Aswani Volety, director of FGCU’s Vester Field Station. “As long as the salinity isn’t in the single digits, they’ll be OK. A little rain wouldn’t be bad, but it could get bad if we get a lot.”
In addition to fresh water, releases bring nutrients to the river and estuary, and excess nutrients can cause harmful micro- and macroalgal blooms — the Olga water treatment plant has been closed since June 5 due to blue-green algae.
“Blue-green algal blooms are characteristic of high-nutrient water,” Milbrandt said. “Increasing flows will increase nutrient loads and could increase the spread of that bloom from where it is now.”
Local commercial fishermen say large releases from Okeechobee hurt the blue crab fishery, which is one of the top 10 commercial fisheries in the state — from 2002 through 2011, Florida’s commercial fishermen harvested an average 9.23 million pounds of blue crab, worth an estimated $9.42 million. Lee County fishermen landed an average 1.11 million pounds of blue crab.
For years, commercial fisherman Mike Grainger of Pine Island harvested blue crabs in the Caloosahatchee River, but, he said, releases from Okeechobee have driven the crabs out of the river during the past few summers.
Now he fishes for blue crab in the St. Johns River near St. Augustine during rainy season and returns to Southwest Florida in the fall for stone crab and mullet.
“Water management in the Caloosahatchee River has affected the crabbing industry,” he said. “Every time they make big releases, they wipe everything out. You might be able to catch a few crabs in the river, but over the last few years, they’ve completely wiped it out. It’s sad.”
Recreational fishermen are also affected by low salinity in the river, said Dave Westra, owner of Lehr’s Economy Tackle in North Fort Myers.
“The detrimental part is salinity levels are too low for baitfish,” Westra said. “In the past couple of summers, we’ve seen if there are freshwater baitfish like tilapia or Mayan cichlids, some redfish and snook will stay around. But most will move down the river to find a better food source in Pine Island Sound, Matlacha Pass or along the beaches.
“As long as water is coming into the lake, they have to dump it, and that isn’t going to help the river.”