The Mouth of Tampa Bay off St. Petersburg

The mouth of Tampa Bay lies southwest of St. Petersburg, in the waters where the U.S. Fish and Wildlife Service locates Egmont Key and, south of it in Manatee County, Passage Key.

The Tampa Bay Estuary Program, whose office is in St. Petersburg at 263 13th Ave. S., describes the estuary and its watershed as stretching from the spring-fed headwaters of the Hillsborough River to the salty waters off Anna Maria Island (Tampa Bay Estuary Program). The federal refuges mark the opening itself: the U.S. Fish and Wildlife Service places Egmont Key National Wildlife Refuge on a remote 250 acre island situated at the mouth of Tampa Bay (USFWS) and says Passage Key is located at the mouth of Tampa Bay in Manatee County, south of Egmont Key (USFWS).

From St. Petersburg, the closest public land on the mouth is Fort De Soto Park in Tierra Verde, the Pinellas County park that runs ferry service to Egmont Key and to Shell Key from its waterfront (Pinellas County). NOAA also lists Tampa Bay PORTS stations at the Sunshine Skyway and in Egmont Channel, covered below.

Tampa Bay is broad but shallow, averaging about 11 feet deep across 400 square miles, while its largest dredged shipping channel, running in through the mouth, is 43 feet deep and 40 miles long.

TBEP calls Tampa Bay Florida's largest open-water estuary and explains why the channel matters: the bay measures only about 11 feet deep on average, so man-made shipping channels have been dredged to allow large ships a safe passageway, and the largest is 43 feet deep and 40 miles long (Tampa Bay Estuary Program). The watershed covers all of Hillsborough County and portions of Pinellas, Pasco, Manatee and Polk counties. At the mouth itself, TBEP says tidal action produces currents of approximately 5.9 ft/s on ebb tides and approximately 3.9 ft/s on flood tides, and salinity in Lower Tampa Bay, nearest the mouth, generally ranges over 25 to 38 ppt (Tampa Bay Estuary Program).

One small inconsistency is worth noting. The same Tampa Bay Estuary Program page calls the 2,200 square mile watershed nearly six times larger than the estuary in one paragraph and more than five times that large in its FAQ; the published figures, 400 and 2,200 square miles, work out to 5.5 times.

Egmont Key, which can be visited, and Passage Key, which is closed year-round, are the two federal refuge islands in the mouth of Tampa Bay, with Pinellas County's Shell Key Preserve and Fort De Soto Park on the St. Petersburg side.

Egmont Key was designated a national wildlife refuge in 1974 and is also cooperatively managed as a unit of the Florida Park Service as Egmont Key State Park; it preserves the remains of historic Fort Dade and an over 100-year-old lighthouse and supports nesting sea turtles, gopher tortoises and over 30,000 nesting pairs of birds (USFWS). Bird sanctuaries at the island's south end make up about one third of Egmont Key, with approximately 97 acres set aside for wildlife.

Passage Key is older as a refuge and far smaller today. President Theodore Roosevelt established it in 1905 to preserve nesting colonies of seabirds and wading birds; once a 60-acre mangrove island with a freshwater lake, it is now a low-lying sandbar that fluctuates in size and is often completely below water at high tide, and it is closed to public use year-round (USFWS). Shell Key, reached only by boat, has a central conservation core closed to the public (Pinellas County); Fort De Soto's hours come from the county park page (Pinellas County).

Ordinary tides at the St. Petersburg gauge rise and fall only about 1.6 feet on average, but NOAA recorded water 6.26 feet above mean higher high water there on September 27, 2024, the station's highest on record.

NOAA station 8726520 in St. Petersburg was established on December 14, 1946, and its present installation dates from March 11, 1991; it lists a mean range of 1.59 ft and a diurnal range of 2.26 ft, a maximum water level of 6.26 ft above mean higher high water on September 27, 2024, and a minimum of 3.82 ft below mean lower low water on September 29, 2022 (NOAA Tides and Currents).

Across the lower bay, the Port Manatee gauge 8726384, established March 24, 1976, keeps a different record: a mean range of 1.54 ft, a record high of 3.58 ft above mean higher high water on August 30, 2023, and a record low of 2.24 ft below mean lower low water on September 28, 2022 (NOAA Tides and Currents). The St. Petersburg record high in 2024 was nearly 2.7 feet above the Port Manatee record.

Conditions for ship traffic through the mouth of Tampa Bay are tracked by NOAA's Tampa Bay PORTS network, which lists 15 stations with water level, current, wave and air gap products, among them Egmont Channel LB 9, Old Port Tampa and Sparkman Channel Entrance.

The PORTS station list includes Sunshine Skyway Bridge Air Gap, Sunshine Skyway Currents, Port Manatee and Port Manatee Currents, Middle Tampa Bay, St. Petersburg, Egmont Channel LB 9 and Egmont Channel Entrance Waves, alongside the Tampa Bay Operational Forecast System and a marine channels forecast (NOAA Tides and Currents).

The traffic is heavy. TBEP says the Port of Tampa consistently ranks among the nation's 10 largest in terms of trade activity, that the average ship calling on Tampa Bay is longer than two football fields, and that on an average day more than 14 million gallons of petroleum products and many other hazardous materials pass in and out of Tampa Bay on ships as large as 48,000 tons, some clearing the bottom by as little as four feet in channels as narrow as 200 feet (Tampa Bay Estuary Program). For small boats leaving St. Petersburg marinas, the practical lesson in the same TBEP guide is that a large ship's ability to maneuver and stop is severely reduced upon entering the narrow confines of harbors such as Tampa Bay.

Federal refuge managers on Egmont Key and Passage Key, Pinellas County at Fort De Soto and Shell Key, and the St. Petersburg based Tampa Bay Estuary Program, which reports on water quality, all have a role at the mouth of Tampa Bay.

The refuges have specific legal purposes. Egmont Key's include providing nesting, feeding and resting habitat for brown pelicans, terns, skimmers and other colonial nesting water birds and protecting endangered species such as sea turtles (USFWS). Passage Key's purpose is nesting, feeding and resting habitat for colonial water birds; more than 50 species have used the sandbar, including nesting American oystercatchers, black skimmers, royal and sandwich terns and laughing gulls (USFWS).

For the water itself, the TBEP report card condenses thousands of water quality records from EPCHC into a yearly status for four segments, from Old Tampa Bay through Hillsborough Bay and Middle Tampa Bay to Lower Tampa Bay, and a 2025 edition is posted (Tampa Bay Estuary Program). TBEP takes public questions at (727) 893-2765 (Tampa Bay Estuary Program).

Last verified: October 18, 2026, against Tampa Bay Estuary Program, U.S. Fish and Wildlife Service, NOAA Tides and Currents and Pinellas County pages.