Mast’s plan for lower lake could hurt St. Lucie estuary

Posted 10/14/20

Martin County residents: Be careful what you wish for.

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Mast’s plan for lower lake could hurt St. Lucie estuary


LAKE OKEECHOBEE — Martin County residents: Be careful what you wish for.

Some residents have voiced support for Congressman Brian Mast’s proposal to lower Lake Okeechobee to less than 11 feet above sea level by June 1 each year.

Mast claims forcing the lake lower would mean more capacity in the lake for the water that drains in from the north during the wet season, and reduce the need for wet season lake releases to the east and west. But had that plan been in place this year, it could have meant more damaging nutrient-rich freshwater releases to St. Lucie estuaries during the hottest months of the year. Those releases would have come not from the lake, but from the C-44 basin.

In mid-May the lake was just above 11 feet. Because the lake was below the current low target level of 12 feet, the U.S. Army Corps of Engineers was in “water storage” mode. So when the heavy rains started in May, the gates on the C-44 canal at Port Mayaca were open, allowing billions of gallons of nutrient-laden water to backflow from the C-44 basin into Lake Okeechobee.

Had the corps been trying to push the lake below 11 feet by June 1, backflowing that water into the lake would have sent the lake level in the wrong direction. Instead, if the goal was to lower the lake, that water could have been released through the St. Lucie lock into the St. Lucie estuary.

Historic data shows the runoff from the C-44 basin is higher in phosphorus than is the water in Lake Okeechobee. Sending that water to tide — instead of backflowing it into the lake —would have lowered the salinity in the estuary and increased the nutrient load, two factors that would have increased the potential for algae blooms in the estuary.

Cyanobacteria, commonly called blue-green algae (although technically not algae), is present in all freshwater unless the system is sterile, according to the Environmental Protection Agency. In the summer of 2020, there were cyanobacterial blooms in Martin County waterways with no releases from the lake. At one point, the Florida Department of Environmental Protection documented a cyanobacterial bloom with high toxin levels in a canal that was emptying into the C-44 just east of Port Mayaca.

Had that local basin runoff gone east into the estuary, it could have increased the chance of blue-green algae problems in the estuary in the hottest months of the summer, when algae blooms are most likely since hot weather is one of the factors that encourage blooms. Instead the water went into Lake Okeechobee, mixing with the vast waters of the second largest freshwater lake within the continental United States, and while the Big O had some algae blooms over the summer, most had no or low levels of toxins.

Stuart officials realized this at the time. In a conference call with the corps, Stuart City Commissioner Merritt Matheson not only expressed thanks to the corps for keeping that C-44 basin water out of the St. Lucie estuary, he even asked if there was some way to pump water from the C-44 canal into the lake when the lake level rose too high to backflow water into the lake by gravity flow.

According to the corps, the freshwater that backflowed into the lake from Port Mayaca during the first months of the summer was the equivalent of about 6 inches on Lake Okeechobee — that’s more than 70 billion gallons of water. (One inch on the lake is about 12 billion gallons of water.)

Now with the lake already over 16 feet — in the danger zone for damaging the lake’s marshes and leaving the Herbert Hoover Dike vulnerable should a hurricane head our way — the corps plans to start releasing water to the St. Lucie at about 1,800 cubic feet per second. Not all of that water will be from the lake. Flow will be measured at the St. Lucie lock so it will include local basin runoff mixed with lake water. Last week the flow averaged about 600 cfs from local basin runoff alone. But even if the entire 1,800 cfs flow was from the lake, consider: 1,800 cfs is about 1,163 million gallons a day. At that rate, it would take about 10 days to equal one inch on Lake Okeechobee, or about 60 days to equal six inches on the lake. So it would take about two months of that level of flow just to return to the C-44 the same amount of water that backflowed from the C-44 earlier this wet season.

It’s already mid-October. There is a good chance the wet season will end before 60 days out. So ... chances are, the St. Lucie will still end the year with less freshwater flow that it would have had if the goal to force the lake below 11 feet by June 1 had been in place. And since that freshwater from the C-44 was stored in the lake during the hottest months of the year, instead of sending it to the coast at that time, the St. Lucie will get that flow at a time of year when it is less likely to cause problems with toxic algae blooms. In addition, the water the C-44 gets back from the lake will be cleaner than the water that backflowed into the lake, due to mixing in the lake with other water.

The C-44 reservoir is currently under construction and when it is complete, it will provide storage capacity for some of that excess water from the C-44 basin. The reservoir will provide 50,600 acre-feet (space for about 16.5 billion gallons). In a year like 2020, that would still mean more than 50 billion gallons of excess freshwater from the C-44 would have to go either east into the lake or west into the St. Lucie estuary.

Is it really best for Martin County if the new Lake Okeechobee regulation schedule requires such a low lake level on June 1 that it removes the option of storing that excess C-44 basin water in the lake?

water level, congressman, St. Lucie estuary