Withlacoochee River System Update - 5/1/2025

Dry Season Lives Up to Its Name

 

Rainfall:

• Our dry season starts in October and ends in June…
• …buts it’s the last couple months (April and May) that are most impactful.
• This time of year, temperatures are high but rainfall is low; the perfect formula for our water resources to decline.
• Average rainfall in April is around 2.8 inches, but last month our region received much less, only 0.8 inches of rain.
• So far this year (January through April), we’ve received about 6.7 inches of rain, half the historical average (12.2 inches) for those first four months.
• And rainfall this year (2025) has been substantially lower than the 12.6 inches of rain we received last year from January through April.
• Not only are our lawns drying up, but our region’s lakes, rivers and aquifer are also declining from lack of rainfall.
• Aquifer (groundwater) levels are now below average, currently in the 49^th percentile for this time of year, and slightly higher than last year (45^th percentile).
• The figure below shows how much rainfall different areas received last month.

 

 

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

• Water levels and flows along the Withlacoochee River continue to decline.
• This is normal for our dry season as the river’s floodplain (swamps, creeks, and wetlands) naturally makes room for wet season rainfall that’s expected this summer.
• Rainfall is the source of water to the Withlacoochee River and each year the river rises and falls depending on how much rain we receive.
• In the Green Swamp, river levels dropped another foot last month and river flows have now ceased.
• Near Trilby (US 301) and Ridge Manor (Hwy 50), river levels also dropped about a foot in April, while flows declined by 50%.
• From Hwy 476 (Nobleton) past Hwy 48, river levels fell about 3 inches last month and flows slowed by 34%.
• Between Hwy 44 and Hwy 200, river levels declined about 9 inches in April, while river flows dropped 52%.
• Without substantial rainfall, river levels and flows will continue to decline until our wet season takes effect later this summer.
• The table below compares current river levels and flows to what they were last month and last year.
• The photo below shows before and after images of the vegetation blockage that was cleared from the Hwy 48 bridge in April.

 

 

Workers Cleared the Vegetation Jam on the Hwy 48 Bridge (April 2025)

 

 

Tsala Apopka Chain of Lakes:

• Water levels on the Tsala Apopka Chain of Lakes will decline about 8 inches per month (¼ inch per day) this time of year if we don’t get any rain.
• The month of April proved this to be true.
• Over the past month, all three pools (including the lakes, wetlands, and canals) fell between 7.2 and 7.8 inches, as the area saw minimal rainfall in April.
• All water control structures remain closed, and no water being discharged from the lakes.
• Water levels are naturally dropping because of high evaporation and continuous leakage downward to the underlying Floridan Aquifer.
• The Floral City and Inverness Pools are currently about 8 inches lower than they were a year ago, while the Hernando Pool is about 2 inches lower than last year.
• Water levels are expected to continue to decline until the summer months bring excess rainfall to the area.

 

Warm Day on the Inverness Pool (April 2025)

 

 

Lake Panasoffkee and Wysong:

• Lake Panasoffkee receives continuous inflow from spring fed creeks (Shady Brook and Little Jones Creek).
• The lake also provides continuous discharges to the Withlacoochee River via the Outlet River.
• Lake levels rise and fall due to several factors including rainfall, creek inflows and outflows which are influenced by Withlacoochee River levels.
• Last month, inflows declined by 36% while outflows fell by 53%.
• Lake Panasoffkee only saw a net drop of ½ inch in April.
• Currently lake levels are about 6 inches lower than they were a year ago.
• The Wysong structure, located 3 miles downstream of Lake Panasoffkee, spans the entire Withlacoochee River.
• The main gate at Wysong (230-foot-wide) remains fully raised while the independent gate (19-foot-wide) is partially raised.
• Wysong is helping to maintain a higher level on Lake Panasoffkee while also passing river flows downstream.
• Both lake and river levels are expected to continue to naturally decline as the dry season continues.

 

 

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) declined by 6% in March.
• Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) declined by 51% last month.
• Overall, inflows to Lake Rousseau are currently 18% lower than they were a year ago.
• Water levels on Lake Rousseau have stayed relatively constant the entire month of April.

 

• As inflows to the lake have declined, outflows have also dropped sharply, about 32% over the past month, due to warmer weather and minimal rainfall.
• Flows that enter Lake Rousseau from the east, exit 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 43% of its capacity.
• When the Bypass Spillway reaches maximum capacity, the Inglis Main Dam discharges excess water from Lake Rousseau to the Barge Canal.
• The Inglis Main Dam remains fully closed and won’t open again until summer rains cause lake inflows to exceed the capacity of the Inglis Bypass Spillway.
• Freshwater flow to the Lower Withlacoochee River is currently about 23% lower than it was a year ago.

 

 

 

Hoping for some rain in May,

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