Water flowing into lake from C-44

OKEECHOBEE — Billions of gallons of nutrient-laden water flowed through the Port Mayaca Lock connecting Lake Okeechobee to the C-44 canal (St. Lucie Waterway) last week. Unlike the same scenario last year, the water flowed from the canal into the lake. And unlike last year, there were no protests, and no footage of the dirty water flowing through the lock on the nightly news.

Flow from the C-44 into the lake was at 2,000 cubic feet per second (cfs) on June 7 and grew to 10,000 cfs on June 9, then dropped down to 852 cfs by June 12 and 380 cfs on June 13.

Between June 1 and June 13, approximately 15 billion gallons of water flowed through the Port Mayaca Lock into Lake Okeechobee.

Billions of gallons of nutrient-laden water flowed through the Port Mayaca Lock connecting Lake Okeechobee to the C-44 canal (St. Lucie Waterway) last week. This photo, taken on June 10 in the morning, shows the gates slightly open on the lake side of the lock with an obvious flow current. Photo by Tom Timmons.

According to SFWMD data, the water in the C-44 canal — which comes from the 185 square mile drainage basin that surrounds the waterway in Martin County — on average is higher in phosphorus than the water in Lake Okeechobee. Nutrient loading into that waterway comes from both urban and agricultural areas. Testing done over the five year period, 2011-2015 by the South Florida Water Management District, found the water in the C-44 averages 154 parts per billion (ppb) of phosphorus.

Florida Department of Environmental Regulations data gives the average phosphorus level in Lake Okeechobee at about 100 pbb. The FDEP target for the lake is 40 ppb. However, with the exception of rainwater (which does contain some phosphorus), every source of water entering the lake is above 40 ppb.

Thus, the water from the C-44 is “polluting” Lake Okeechobee.

Water from that basin does not often flow into the lake — this can only happen when the lake level is lower than the water level in the canal. During wet years — such as 2016 — no water from the C-44 entered the lake. On average, according to SFWMD data, drainage into the C-44 canal makes up about 4 percent of the water entering the lake and also about 4 percent of the phosphorus entering the Big O each year.

By comparison, water entering the big lake from the communities south of the lake account for about 3 percent of the water and about 4 percent of phosphorus. Water normally flows south, but in extreme rain conditions, water is backpumped from areas south of the lake to alleviate flooding in the towns there.

Thus, water from the C-44 is “polluting” the lake at about the same average amount that the area south of the Big O “pollutes” the lake — which is, considering the amount of water in the 40-mile wide lake, not considered a significant problem by water managers. In both cases, if the lake level is low enough, moving the floodwater into the lake is deemed the least harmful of the available choices. If they could not move water to the lake, the choices in Martin County would be either to send the water to the coastal estuaries or else let the area flood. South of the lake, if they could not backpump, the towns on the south end of the Big O would face flooding. When the rain is sufficient to flood the towns, water can’t be moved south because the areas south of the lake are already inundated, and flow to Florida Bay cannot be increased until more of the Tamiami Trail is raised to allow more flow.

Phosphorus levels in Lake Okeechobee vary. Along the shoreline, where plants absorb nutrients, the phosphorus levels are lower. In the middle of the lake, phosphorus levels tend to be higher, and FDEP research shows there is an accumulation of phosphorus in the muck in the lake sediment near the center of the lake. Events such as hurricanes, which can stir up the sediment at the bottom of the lake, cause the phosphorus levels in the water to increase. Raising the lake level above 16 ft. damages the marshes around the edge of the lake and causes the phosphorus levels in the lake to rise.

When the lake level is lower, phosphorus levels drop. Records show that in 2012, following a multi-year period of lower lake levels, phosphorus levels in the middle of the lake were 92 ppb and phosphorus levels near the shore dropped to 41 ppb.

The other sources of water — and of phosphorus — entering the lake range from 69 ppb to 456 ppb according to SFWMD data.

The highest phosphorus concentration comes from Taylor Creek/Nubbin Slough, which accounts for only 6 percent of the water entering the lake but on the average contributes 19 percent of the phosphorus. The source of phosphorus can be difficult to track. At one time, it was believed the high phosphorus levels in that waterway were due to runoff from dairies in the watershed. But in 1986, the FDEP Dairy Rule forced the dairies to either move out of the basin or recycle their wastewater and contain the runoff. Yet while dairies have not been contributing runoff to the waterway for the past 30 years, the phosphorus levels have not lessened.

Port Mayaca Lock and Dam on the lake side with water flowing from the canal into the lake.

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