Withlacoochee River System Update - 10/1/2025

Water Levels Decline as Dry Season Begins

 

Rainfall:

• While hurricane season continues for a couple more months, our wet season has officially ended.
• During the summer months (June – September) we average 6-8 inches of rain per month.
• But starting in October, rainfall totals drop off sharply, with a monthly average of only 2-3 inches of rain from now until next summer.
• In September, our region received just 3.3 inches of rainfall, about half the historical average for the month (6.3 inches).
• So far this year (January through September), we’ve only received 36 inches of rain, 10 inches below the historical average (46 inches) for the first 9 months of the year.
• This time of year (end of the wet season) our water levels are typically their highest and will slowly decline over the next 8 months.
• We really didn’t get much rainfall during our wet season this year and water levels are already starting lower than normal as our dry season begins.
• Of course, a couple late-season tropical storms could still turn things around.
• Aquifer (groundwater) levels remain below average, currently in the 29^th percentile for this time of year, and much lower than last year (68^th percentile). Remember, the 50^th percentile is average.
• Lower aquifer levels affect our lakes, rivers, and wetlands by allowing those surface water bodies to drain down into the ground faster.
• The figure below shows how much rainfall different areas received last month. The green and blue areas received above average rainfall in September.

 

 

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

• Time is running out for the Withlacoochee River to rise this year.
• Heavy rainfall during the summer months normally causes the Withlacoochee River to rise and peak this time of year.
• But that rainfall hasn’t materialized, and the Withlacoochee could see much lower levels in the drier months ahead.
• Flow from the Green Swamp is nearly non-existent, a condition in early October that we’ve only seen 3 times in the last 30 years.
• Downstream near Trilby (US 301) and Ridge Manor (Hwy 50), river levels and flows are once again declining, after only rising a couple feet this summer.
• In this stretch of the river, water levels are 12 feet lower than they were last October, and that was even before Hurricane Milton arrived.
• Near Nobleton (Hwy 476) and Bushnell (Hwy48), river levels and flows are also slowly dropping, and are currently about 2-3 feet lower than they were a year ago before Milton.
• From Hwy 44 to SR 200, river levels and flows crested a few weeks ago and are also declining. River levels in these areas are currently 3-5 feet lower than last October (before Milton).
• The table below compares current river levels and flows to what they were last month and last year.

 

 

Withlacoochee River near Hwy 200 (September 2025)

 

 

Tsala Apopka Chain of Lakes:

• The Tsala Apopka Chain of Lakes saw a slight rise in water levels during the month of September.
• The Floral City Pool rose 1.5 inches, the Inverness Pool rose 4.1 inches, and the Hernando Pool rose 2.3 inches.
• Those gains were caused by scattered rainfall throughout the lake chain combined with river inflows.
• Water control structures, which were opened in July, remain open evenly sharing available river water between all three pools.
• But river levels have been low this year, so very little flow has entered the lakes, and what has entered has been offset by evaporation and downward leakage to the underlying aquifer.
• The Leslie Heifner and Floral City structures remain fully open, moving water into the Floral City Pool.
• The Golf Course and Brogden Bridge structures are also open, evenly splitting those flows with the Inverness and Hernando Pools.
• As river levels continue to drop, less water will be available to flow into the lakes and once river levels fall below lake levels, the structures will be closed again.
• All three pools are currently about 1 ½ feet lower than they were a year ago, and 2 feet lower than the high levels we typically see at the end of the wet season.

 

Sunrise on the Tsala Apopka Chain of Lakes (October 1, 2025)

 

 

Lake Panasoffkee and Wysong:

• Across the river in Sumter County lies Lake Panasoffkee, a spring-fed lake influenced by regional rainfall and the Withlacoochee River.
• After steadily rising since early July, the water level on Lake Panasoffkee finally peaked in mid-September and has begun slowly declining in recent weeks.
• Spring-fed creeks, that also convey rainfall runoff into the lake, have been flowing strong for the past couple months due to higher rainfall east of Lake Panasoffkee.
• Outflow from Lake Panasoffkee to the Withlacoochee River also remains strong.
• The Wysong structure, located 3 miles downstream of Lake Panasoffkee, spans the entire Withlacoochee River.
• The main gate (230-foot-wide) of Wysong remains raised.
• The independent gate (19-foot-wide) is partially lowered, allowing river flows to pass downstream.
• Water levels and flows in this area will continue to steadily decline unless the region receives widespread heavy rainfall in the coming weeks.
• Lake Panasoffkee water levels are currently about 4 inches lower than they were a year ago, and 3 feet lower than the peak from Milton last fall.

 

 

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) increased by 1% last month.
• Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) decreased by 6% in September.
• Flows entering Lake Rousseau are currently 61% lower than a year ago, because of less rainfall in 2025.
• Water levels on Lake Rousseau have stayed relatively constant the entire month of September.

 

• Flow that enters Lake Rousseau from the east, exits through water control structures on the west end of the lake.
• There are two structures that release water from the lake (see map below).
• The primary outlet from Lake Rousseau is the Inglis Bypass Spillway which provides continuous freshwater flow to the Lower Withlacoochee River.
• The Inglis Bypass Spillway is currently flowing at 56% of its capacity, down 11% from last month.
• When the Bypass Spillway reaches maximum capacity, the Inglis Main Dam is opened, discharging excess water from Lake Rousseau to the Barge Canal.
• This provides flood protection to the Lower Withlacoochee River when the river upstream of Lake Rousseau is experiencing high water conditions.
• Coastal flooding from storm surge (high ocean levels) is not preventable by any water control structures.
• The Inglis Main Dam, which closed in early February, remains fully closed and won’t open again until Withlacoochee River flows increase substantially (likely next summer).
• Last year at this time, the Inglis Main Dam was open, discharging nearly a billion gallons of water a day in the Gulf.
• Freshwater flow to the Lower Withlacoochee River is only one-quarter of what it was a year ago.

 

 

 

Have a wonderful rest of the week!

Mark

 

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