The Tampa Bay Watershed

The Tampa Bay watershed covers 2,200 square miles, nearly six times the area of Tampa Bay itself, and takes in all of Hillsborough County plus parts of Pinellas, Pasco, Manatee and Polk counties (Tampa Bay Estuary Program, About the Bay).

Every storm drain in Tampa sits inside that boundary. Rain that falls anywhere within it eventually reaches Tampa Bay through creeks, rivers, lakes or pipes, which is why a lawn in Brandon or a parking lot in Westshore counts as part of the same system as the bay shoreline (TBEP).

The bay the land drains to is shallow. The Tampa Bay Estuary Program lists an average depth of 11 feet and a maximum of 43 feet, and more than 80 miles of shipping channels, some cut as deep as 43 feet, cross the open water (TBEP, About the Bay).

The program counts the land as 42 percent urban and suburban, 32 percent undeveloped, 17 percent agriculture and 9 percent mining (TBEP). Agriculture and mining together account for about a quarter of the land draining to Tampa Bay.

Four rivers, the Hillsborough, Alafia, Little Manatee and Manatee, supply about 70 to 85 percent of the roughly 525 billion gallons of fresh water that reach Tampa Bay in a year (Tampa Bay Estuary Program).

The Hillsborough River is the one that runs through Tampa. The Southwest Florida Water Management District lists it as rising in the Green Swamp of southeast Pasco County, running 55 miles, draining 690 square miles and meeting the bay at Hillsborough Bay, with tributaries that include Crystal Springs, Blackwater Creek, Flint Creek, Trout Creek, Cypress Creek, Curiosity Creek and Sulphur Springs (SWFWMD, Four Rivers Emerge). The Hillsborough River guide covers that river in detail.

Where the rivers enter changes how salty each arm of the bay is. The estuary program gives typical ranges for three segments, and Hillsborough Bay, where the Hillsborough River empties, runs the freshest (TBEP, About the Bay).

Stormwater runoff from urban and residential land now delivers more than half of the nitrogen entering Tampa Bay, according to the Tampa Bay Estuary Program, making the watershed itself the largest source (TBEP, About the Bay).

About one-quarter of the nitrogen load reaches Tampa Bay from the air, mainly from power plants and automobiles, and wastewater treatment plants and industrial discharges are now relatively small sources (TBEP). Stormwater carries fertilizer and pesticide residue and trash off the land with each rain.

Sewage used to be the problem. The estuary program says improvements to sewage treatment plants in the 1970s cut the nitrogen in effluent by more than 90 percent, which cleared the water and started a seagrass recovery in Tampa Bay (TBEP, About the Bay).

The water quality guide covers what the state measures in Tampa waters and which segments are listed; this page stays with the land that drains to them.

The Tampa Bay Estuary Program and the Southwest Florida Water Management District publish different numbers for the size of Tampa Bay, the watershed population, the counties involved and the year of the federal designation, and neither page explains the gap (SWFWMD, Tampa Bay SWIM).

The Tampa Bay Estuary Program also disagrees with itself on the plan date: its About the Bay page says the management plan was adopted in 1997 (TBEP), while its plan timeline says the first Comprehensive Conservation and Management Plan was approved in 1996 by local partners, the Governor and the EPA Administrator (TBEP, Explore the Plan).

The estuary program's own About the Bay page also gives two population figures, more than 3.1 million in its quick facts and approximately 3 million in its text, and describes the watershed as nearly six times the bay in one paragraph and more than five times in another (TBEP, About the Bay). The watershed area of 2,200 square miles is the one figure in the table that both Tampa Bay agencies give, and SWFWMD dates the federal designation to 1990, a year earlier than the 1991 date on the estuary program timeline.

The Tampa Bay Estuary Program coordinates restoration across the watershed as a partnership of Hillsborough, Manatee, Pinellas and Pasco counties, the cities of Clearwater, St. Petersburg and Tampa, the Florida Department of Environmental Protection, SWFWMD and the EPA (TBEP, About the Bay).

Tampa Bay is one of 28 estuaries the EPA lists as estuaries of national significance under the National Estuary Program (EPA, Local Estuary Programs). A 1998 Interlocal Agreement among the partners made the Tampa Bay Estuary Program an independent special district of the State of Florida, and the public and private Tampa Bay Nitrogen Management Consortium, formed in 1996, works on the nitrogen targets tied to seagrass goals (TBEP plan timeline).

The current plan, Charting the Course, sets out 16 action plans, 38 actions and 163 activities to keep Tampa Bay restoration going through 2027 (TBEP, Explore the Plan). On the state side, the Florida Legislature created the Surface Water Improvement and Management (SWIM) Act in 1987, and SWFWMD lists Tampa Bay first among its 12 SWIM priority water bodies, which also include Lake Thonotosassa in Hillsborough County (SWFWMD, About SWIM).

The district Tampa Bay SWIM goals include updating nutrient reduction goals for each bay segment, proposing segment specific seagrass light targets and supporting the 2030 targets in the 2020 Habitat Master Plan, under the 2023 SWIM Plan; one stated measure of success is recovery of seagrass to 2020 levels (SWFWMD, Tampa Bay SWIM).

Inside Tampa city limits, lawn and landscape fertilizer containing nitrogen or phosphorus may not be applied from June 1 through September 30 under the City of Tampa fertilizer ordinance (City of Tampa, Fertilizer Management).

The Tampa ordinance adds to the Environmental Protection Commission of Hillsborough County rule, which requires training and certification for commercial fertilizer applicators, bans putting grass clippings, fertilizer and yard waste in the street, sets a 10-foot fertilizer free zone near water and requires a deflector shield on spreaders (City of Tampa).

Outside the city, Hillsborough County Ordinance 21-42 bars nitrogen and phosphorus fertilizer between June 1 and September 30 in unincorporated Hillsborough County, and the county page notes that the City of Tampa has a different but similar ordinance (Hillsborough County, Fertilizer Ordinance). The county ordinance is in addition to the EPC Chapter 1-15 Fertilizer Use and Landscape Management Rule, in effect since June 2010, and supersedes it, although anything in the EPC rule that the ordinance does not contain is still in effect.

Last verified: October 18, 2026, against the Tampa Bay Estuary Program, the Southwest Florida Water Management District, the City of Tampa and Hillsborough County websites.