Hillsborough River Dam and Reservoir — Tampa, Florida

The Hillsborough River Dam is the City of Tampa's water supply dam on the lower Hillsborough River in Sulphur Springs. Behind it lies what the City of Tampa Water Department calls the 1.2 billion gallon Hillsborough River Reservoir, the city's primary drinking water source. The dam turns the river above Sulphur Springs into a long, narrow pool from which the David L. Tippin Water Treatment Facility, on the riverbank near 30th Street, draws its raw water.

A federal study gives the engineering outline. The U.S. Geological Survey Water-Resources Investigations Report 78-29 describes the Tampa Reservoir Dam as built in 1945 on the lower Hillsborough River 10 miles above its mouth, holding 12.5 miles of the natural river channel as storage. The present structure replaced an earlier dam at the site owned by the Tampa Electric Company, whose failure in 1933 is part of Sulphur Springs history.

Tampa began with private water. The City of Tampa history slideshow records that the town's population in 1882 was 499 and that its first water company was Tampa Water Works, a private company, with published water rates and rules dating to 1892. According to the Water Department's 1926 production plant page, after that early privately owned company had difficulty giving a growing city a reliable supply of drinking water, city leaders built a municipal water treatment plant on the banks of the Hillsborough River in an area that was then remote.

The river was the obvious source because of where it comes from. The Tampa Water Department treatment process page explains that by the time Hillsborough River water reaches the plant it has traveled over 50 miles southwest from the Green Swamp, and that its tea-like color comes from natural organic matter released by decomposing vegetation in the swampy flatlands. The department reports delivering 82 million gallons of water a day to close to 717,000 people, which is the demand the Sulphur Springs dam and reservoir are built to meet.

Before the city controlled the river, Tampa Electric Company operated a dam on the Hillsborough River at Sulphur Springs. WUSF Public Media reported in November 2019 that everything changed for the Sulphur Springs resort district in 1933, when the collapse of the Tampa Electric Company dam destroyed the arcade. The flood that followed is a turning point in accounts of the neighborhood, which lost much of its tourist trade in the 1930s.

The City of Tampa's water history slideshow picks up the story with an image captioned TECO Dam and the note that the dam was rebuilt in 1944. USGS dates the completed Tampa Reservoir Dam to 1945, so the rebuilding spanned 1944 and 1945. The slideshow adds that 1960 flooding in Tampa damaged the dam and that new crest tainter gates were installed on it in 1963 and 1964.

The dam sits beside an older city investment. The Water Department records that in 1924 construction began on a water treatment plant on the Hillsborough River near 30th Street, and that the original filter house, completed in 1925, is still in use after several expansions. The plant is designated an American Waterworks Landmark, and the city notes that its original high speed pumps, once driven by steam turbines, now run on electric motors.

Figures differ by date and method. The 1976 USGS study calculated that, excluding dead storage, Tampa Reservoir capacity is 2,000 million gallons at a maximum stage of 22.5 feet above mean sea level. The City of Tampa's current description, on a Water Department page updated October 1, 2023, gives the Hillsborough River Reservoir as 1.2 billion gallons.

USGS also measured how reliable the reservoir is in drought. Flow of the lower Hillsborough River and storage behind the Sulphur Springs dam become deficient during annual dry periods, the report found, and in any year at full capacity Tampa Reservoir and the river have a 5 percent chance of failing to supply at least 66 million gallons of water per day and a 2 percent chance of failing to supply at least 59 million gallons per day.

Those limits explain the backups described on the Tampa Water Department About Us page. The Tippin plant can produce up to 120 million gallons a day at peak and averages 82 million gallons a day over a year. When excess water is available, up to 1.2 billion gallons is stored in the city's Aquifer Storage and Recovery System, and when the river cannot meet demand in extended dry periods, Tampa buys treated groundwater, surface water and desalinated seawater from Tampa Bay Water.

The dam holds water for drinking, but it sits downstream of a federal flood control network run by the Southwest Florida Water Management District (SWFWMD). SWFWMD's WaterMatters magazine for November to December 2004 explains that the Harney Canal and Structure 161 were built to divert runoff from the 192-square-mile drainage area between the Lower Hillsborough Flood Detention Area and the Hillsborough River Reservoir Dam. District staff work with the City of Tampa to decide how much water to divert, striking a balance between flood protection and keeping appropriate levels in the city's water supply reservoir.

The SWFWMD Tampa Bypass Canal System page places the Harney Canal a few miles north of the City of Tampa's dam and says the canal is opened when inflows below the District's earthen dam cause river flooding. That route is especially useful when discharges from the city's Hillsborough River Dam are impeded by storm surge from a hurricane, since high water in the bay can block outflow through Sulphur Springs and downtown Tampa.

The structure needs periodic repair. The City of Tampa Contract Administration office posted bid 21-C-00012, Hillsborough River Dam North Embankment Remediation, on January 27, 2021, with bids opened on March 16, 2021, and posted an award document on the same project page.

Drought puts the reservoir at the center of Tampa water rules. The city's watering days page states that Tampa's water use restrictions have been in place and enforced year-round since 1992, and that a Modified Phase III Water Shortage Order was passed by SWFWMD on March 24, 2026. Tampa Water Department pages showed a Modified Phase III Extreme shortage status effective April 3, 2026.

Low, warm reservoir water also shows up at the tap. The City of Tampa water FAQs explain that a lack of rainfall combined with rising daytime temperatures can cause algae blooms in the Hillsborough River Reservoir that temporarily give Tampa's water an earthy taste and odor while it is being treated. The same FAQs report that hardness of water drawn mainly from the Hillsborough River ranges from about 140 to 300 parts per million, lower in the wet season and higher in the dry season.