From May 31 to July 6, about 16.5 billion gallons of water flowed into Lake Okeechobee at Port Mayaca, according to SFWMD records.
Flow of water from the St. Lucie waterway into the lake — instead of the other direction — was possible because a drought had left the lake level lower than the water level in the C-44 canal. At its peak, the water at the Port Mayaca Lock was flowing at more than 10,000 cubic feet per second (cfs) into the lake. For comparison, in 2016, when flow was 2,000 cfs, Treasure Coast residents were protesting the water flowing through that same lock in the other direction.
Had water managers not allowed that untreated water into the lake, that 16.5 billion plus gallons of nutrient-rich runoff from the St. Lucie watershed would have poured into the St. Lucie estuaries.
“The backflow of water at Port Mayaca was beneficial to the estuaries,” said SFWMD’s Randy Smith. Flowing the water into the lake, instead of letting it go to tide, protected the estuaries from that heavy, nutrient-laden freshwater flow.
While some Treasure Coast residents like to blame the lake for the high phosphorus and nitrogen content in their waterways, SFWMD and University of Florida Water Institute data shows the runoff from the St. Lucie watershed is actually higher in nutrient load than the flow from the lake. A 5-year average found runoff from the C-44 watershed to be about 154 ppb (parts per billion) phosphorus while water from the lake, according to the Florida Department of Environmental Regulation (FDEP) averages around 100 ppb.
It must be noted that the phosphorus levels in the lake vary widely depending on where the measurements are taken, and the depth of the lake at the time measurements are taken. When the lake level rises, so does the phosphorus level.
Also consider that the heavy flow of water in the St. Lucie watershed in June, which flushed out the canals in the watershed after the drought, was likely to be even “dirtier” than average.
That flow from the St. Lucie watershed continues, although at a lesser pace than in June, so that the total gallons will continue to rise. On July 11, the flow at Port Mayaca into the lake was averaging 420 cfs.
South of the lake, an environmental emergency lead to a decision to pump water north from the Everglades into the Big O to protect wildlife from flooding in the water conservation areas (WCAs).
South Florida experienced an unprecedented level of rainfall in June. The Florida Fish and Wildlife Conservation Commission (FWC) closed Water Conservation Area 3 (WCA-3) to recreational activities due to the more than 15 inches of rain received across that region.
The rain was actually heavier in the southern part of the Everglades, Mr. Smith pointed out.
The Everglades Agricultural Area, just south of the lake, received about 15 inches of rain in June. The area south of the EAA received in excess of 18 inches of rain. Some water conservation areas (WCAs) received more than 22 inches of rainfall. According to FDEP, the rainfall in some areas qualified as a 100-year storm event.
Lowering the water levels in the WCAs south of the EAA was critical not only to wildlife but also to protect the urban residents along the east coast, Mr. Smith said. The rising water levels could have threatened the East Coast Protective levy, which holds back flow from the Everglades into the urban area that was once part of the Everglades.
Mr. Smith said they worked with farmers to try to minimize the mix of the flow being pumped into the canals from the south with the runoff from the agricultural fields. Some mixture was inevitable, he said, but tests showed the water being backpumped into the lake was relatively low in phosphorus. Most of the water pumped north had already been treated by flowing it through marshes which absorb some of the nutrients from the water. He said the farmers own efforts in reducing phosphorus in the runoff from fields have improved every year.
Backpumping water from south of the lake stopped on July 3.
Water from the WCAs south of the EAA originally flowed into Everglades National Park, but the berm created by the Tamiami Trail blocks the natural sheet flow. One mile of bridging allows some flow under the road; 2.5 additional miles of bridging are under construction.
Due to the emergency situation, water flow through existing water control structures that allow flow south was increased, despite objections from the U.S. Fish and Wildlife Service which tried to block any increase in flow until the end of the nesting season for the Cape Sable Sea Sparrow in mid-July.