Today, the area is home to about 4 million residents, making Tampa Bay a heavily used commercial and recreational waterway and subjecting it to increasing amounts of pollutants from industry, agriculture, sewage, and surface runoff.

Greater care has been taken in recent decades to mitigate the effects of human habitation on Tampa Bay, most notably upgraded sewage treatment facilities and several sea grass restoration projects, resulting in improved water quality over time.

Local marketing and branding efforts (including several professional sports teams, tourist boards, and chambers of commerce) commonly use the moniker "Tampa Bay", furthering the misconception that it is the name of a particular municipality when this is not the case.

[2][3] Tampa Bay formed approximately 6,000 years ago as a brackish drowned river valley type[4] estuary with a wide mouth connecting it to the Gulf of Mexico.

[5] Though the exact process of the lake-to-bay transformation is not completely understood, the leading theory is that rising sea levels following the last ice age coupled with the formation of a massive sink hole near the current mouth of the bay created a connection between the lake and the gulf.

[6] Tampa Bay is Florida's largest open-water estuary, extending over 400 square miles (1,000 km2) and forming coastlines of Hillsborough, Manatee and Pinellas counties.

[9] The relatively shallow water and tidal mud flats allow for large sea grass beds, and along with the surrounding mangrove-dominated wetlands, the bay provides habitat for a wide variety of wildlife.

More than 200 species of fish are found in the waters of the bay, along with bottlenose dolphins and manatees, plus many types of marine invertebrates including oysters, scallops, clams, shrimp and crab.

The cooler months are also when warm-water outfalls from power plants bordering the bay draw one out of every six West Indian manatees, an endangered species, to the area.

Heavy harvesting of fish and other sea life, constant dredging of shipping channels, and the clearing of mangroves for shoreline development were important factors.

The water was so murky that sunlight could not reach the shallow bottom, reducing sea grass coverage by more than 80% compared to earlier in the century and severely impacting the marine ecosystem.

For example, in 2004, a leak of 65 million gallons of acidic water from a Cargill phosphate plant on the bay's southern shore severely impacted wetlands in the vicinity of the spill.

[19] And in April 2021, a breach of a wastewater reservoir at the long-closed Piney Point phosphate plant sent over 200 millions gallons of nutrient-rich mine tailings streaming into lower Tampa Bay.

[20] The resulting growth of red tide algae led to an ecocide and killed over 1000 tons of fish in the bay and along the nearby gulf coast and may lead to further damage to seagrass beds.

[30] Evidence of human habitation from this early period has been found at the Harney Flats site, which is approximately 10 miles east of the current location of Tampa's downtown waterfront.

The Tocobaga, who built their principal town near today's Safety Harbor in the northwest corner of Old Tampa Bay, are the most documented group from that era because they had the most interactions with Spanish explorers.

[35] Not finding gold or silver in the vicinity and unable to convert the native inhabitants to Christianity, the Spanish did not remain in the Tampa Bay area for long.

Fort Brooke begat Tampa on the northeast shore, Fort Harrison (a minor military outpost on Florida's west coast) begat Clearwater, the trading post of "Braden's Town" developed into Bradenton on the south, and St. Petersburg grew quickly after its founding in the late 19th century, on the western bay shore opposite Tampa.

A deep shipping channel was created which linked Port Tampa to the mouth of the bay, enabling Plant to greatly expand his steamship line.

The difficulty of traveling between Tampa and St. Petersburg in the early 20th century inspired the world's first scheduled air service, the St. Petersburg-Tampa Airboat Line, which operated during the tourist season of 1914.