Withlacoochee River Back to Normal as Dry Season Continues

Rainfall:

• 2024 was an above average year for rainfall.
• The Withlacoochee River Watershed normally receives about 53.5 inches of rain per year.
• Last year (2024) our region averaged 57.1 inches, including about an inch of rain in December; but you can see in the graphic below that some areas received even more than that.
• An active wet season (June-September), capped off with heavy rainfall from Hurricane Milton (October) caused widespread flooding throughout our region.
• More than two months later, water levels have dropped considerably, but many areas remain wetter than normal for this time of year.
• Aquifer (groundwater) levels are still high, currently in the 83rd percentile for this time of year, much higher than last year (52nd percentile).
• The figure below shows how much rainfall different areas received in 2024. Most areas saw above average rainfall last year (green, blue, and purple).
• As we start a new year, it’s unclear what 2025 has in store for us. But we can bet our region’s lakes, rivers and the aquifer will respond according to how much or little rainfall we end up getting.

Withlacoochee River (from the Green Swamp downstream past Hwy 200):

• For the second month in a row, water levels and flows have substantially declined along the entire Withlacoochee River.
• River flows dropped by 60% in December.
• In the Green Swamp, river levels fell another 0.5 to 1.1 feet in last month.
• Near Trilby and Ridge Manor, river levels dropped 3 feet in December.
• Near Nobleton (476) and Hwy 48, the river fell more than a foot in December.
• At Hwy 44 and Hwy 200 (Holder), the river dropped 2 feet and 3.5 feet, respectively, last month.
• Many areas that were flooded by high water from the Withlacoochee River after Milton, remain high with nowhere to drain except evaporation or seepage downward.
• The table below compares current river levels and flows to what they were last month and last year.
• Overall, river levels and flows are higher than they were a year ago.

Tsala Apopka Chain of Lakes:

• Stagnant water bodies including lakes, ponds and wetlands will decline much slower than flowing rivers and streams.
• All three pools of the Tsala Apopka Chain of Lakes dropped about 2-3 inches last month due to minimal rainfall.
• There is currently no flow of water entering the lake chain since the Withlacoochee River is lower and dropping quicker.
• All the water control structures in the lake chain remain closed, helping to conserve water in the vast network of lakes, canals, and freshwater marshes.
• Despite no water flowing in or out, water levels will decline every day there’s no rain, because of evaporation and downward leakage to the underlying aquifer.
• Currently all three pools are more than a foot higher than they were last year at this time.

Lake Panasoffkee and Wysong:

• Water levels on Lake Panasoffkee rise and fall every year due to ever-changing inflows to and outflows from the lake.
• Two major creeks, Shady Brook and Little Jones Creek bring constant spring-fed flow into the lake, which also receives water directly from an aquifer that is higher than the lake level itself.
• Lake Panasoffkee provides continuous outflow to the Withlacoochee River through the 2-mile-long Outlet River that connects the two water bodies.
• Lake levels declined 8 inches the first half of December but have held relatively steady since then due to inflows equaling outflows and the Withlacoochee River returning to its normal level.
• Creek inflows changed very little over the past month while outflows are 50% less than they were at the start of December.
• About three miles downstream from Lake Panasoffkee, the Wysong structure spans the entire width of the Withlacoochee River.
• After being fully lowered for more than 4 months, the main gate of the Wysong structure was finally raised again in mid-December after Withlacoochee River levels returned to normal.
• The smaller, independent gate at Wysong remains fully lowered allowing river flows to pass downstream.
• River flows at Wysong have declined 67% over the past month.
• Lake Panasoffkee is currently 5 inches lower than it was a year ago.

Lake Rousseau and the Lower Withlacoochee River (from Dunnellon to the Gulf of Mexico):

• Downstream of Dunnellon, the Withlacoochee River enters Lake Rousseau, an in-stream lake formed over a century ago with flood control structures near Inglis.
• Inflow to Lake Rousseau includes combined flows from the Withlacoochee and Rainbow Rivers.
• Rainbow River flow (which reflects changes in aquifer levels) fell 15% in December.
• Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) decreased 55% last month.
• Overall, inflows to Lake Rousseau have declined substantially over the past month but remain 40% higher than they were a year ago.
• Water levels on Lake Rousseau have stayed relatively constant the entire month of December.

• All flows entering Rousseau from the east are exiting through water control structures on the west end of the lake.
• The primary outlet from lake Rousseau is the Inglis Bypass Spillway which provides continuous freshwater flow to the Lower Withlacoochee River.
• This structure, which has discharged maximum available flow since early August, remains fully open with 35% more flow than a year ago.
• The Inglis Main Dam, which was opened in early August, remains open discharging excess water from Lake Rousseau to the Barge Canal.
• Last year at this time the Inglis Main Dam was closed.
• The Inglis Main Dam will remain open until the Inglis Bypass Spillway is able to pass all incoming flows, which may not happen for another month or two.

Mark Fulkerson, Ph.D., P.E.

Chief Professional Engineer

Southwest Florida Water Management District

 (352) 269-6073 (office)

(352) 279-4493 (cell)

Mark.Fulkerson@WaterMatters.org

 Withlacoochee River Watershed Initiative