Biscayne Bay (Bahía Vizcaina, in Spanish) is a lagoon that is approximately 35 miles (56 km) long and up to 8 miles (13 km) wide located on the Atlantic coast of south Florida. It is usually divided for purposes of discussion and analysis into three parts, North Bay, Central Bay and South Bay.
North Bay separates Miami Beach on its barrier island from Miami on the mainland. It has been severely affected over the last century by raw sewage releases, urban runoff, shoreline bulkheading, dredging, the creation of artificial islands and the loss of natural fresh water flow into the bay. North Bay accounts for only 10% of the water area of the bay.
Central Bay is the largest part of the bay. It is separated from the Atlantic Ocean by the Safety Valve, a series of shallow flats separated by tidal flow channels, stretching from the south end of Key Biscayne to the Ragged Keys at the north end of the Florida Keys. It has been adversely affected primarily by bulkheading, urban runoff discharged by canals, and the loss of natural fresh water flow.
South Bay is nearly as large as Central Bay, and is the least affected by human activities, although it also suffers from the loss of natural fresh water flow. South Bay is separated from the Atlantic Ocean by the northernmost of the Florida Keys, and is connected to Florida Bay through channels and "sounds" lying between the mainland and the keys.
The first bridge across Biscayne Bay was the 2.5 mile wooden Collins Bridge built by John S. Collins and Carl G. Fisher. The toll bridge was "the longest wooden bridge in the world" when it was completed in 1913 at the southern terminus of the Dixie Highway. The Collins Bridge was replaced in 1925. In modern times, the Venetian Causeway follows the same route along the artificial Venetian Islands. The MacArthur, Julia Tuttle, 79th Street and Broad causeways connect Miami to Miami Beach, and the Rickenbacker Causeway connects Miami to Key Biscayne. The Card Sound Bridge connects the mainland in the Homestead, Florida area to the northern part of Key Largo. The bay is home to Biscayne National Park. The seven remaining houses of Biscayne Bay's Stiltsville settlement are now within the boundaries of this National Park.
The bay has been known by several names. Juan Ponce de Leon called it Chequescha in 1513. Pedro Menéndez de Avilés called it Tequesta in 1565. The British, during their occupation of Florida, called the bay Cape River, Dartmouth Sound, and Sandwich gulph. Hernando de Escalante Fontaneda related that a sailor from the Bay of Biscay called the Viscayno or Biscayno had lived on the lower east coast of Florida for a while after being shipwrecked, and a 17th century map shows a Cayo de Biscainhos, the probable origin of Key Biscayne. The bay was known as Key Biscayne Bay in the 19th century, finally shrinking to Biscayne Bay late in the 19th century.
The bay is also home to Florida International University's Biscayne Bay Campus in North Miami.