Bahía Blanca is a city in Buenos Aires Province, eastern Argentina, and a seaport at the head of the Bahia Blanca ('White Bay' - an arm of the Atlantic Ocean) at the mouth of the River Naposta. It has a population of 274,509 (2001 census) and is the capital of the Bahía Blanca Partido.

The city was founded as a fort in 1828, the Fortaleza Protectora Argentina ('Argentine Protective Fortress'), to protect cattle from native rustling and to protect the coast from Brazil's navy who had landed in the area the previous year. The fortress was attacked by the aboriginal malones (mounted incursion forces) several times, most notably in 1859 by 3,000 Calfucurá warriors. It became commercially important after the construction of a railroad through the area in 1885 to connect the town with the cereal-growing interior, attracting many European immigrants.

Bahía Blanca is an important trans-shipping and commercial center, handling the large export trade in grain and wool from southern Buenos Aires Province, oil from Neuquén Province, and fruit from the Río Negro Valley. Its seaport is one of the most important in the country, being the only one that is a naturally 10-metre (33 feet) deep port. Along the bay, the ports are Puerto Ingeniero White for grain, and Puerto Galván, a smaller one specialising in oil and chemicals. Between these two main ports, several agro-industrial and chemical plants operate their own piers. Puerto Belgrano, 29 km southwest, is Argentina's largest naval base.

The National University of the South (Universidad Nacional del Sur) (founded 1956) is in Bahía Blanca. The neoclassical cathedral is the seat of the Archdiocese of Bahía Blanca, which covers dioceses across the whole of Patagonia and Tierra del Fuego, with its own diocese in the south of the Province of Buenos Aires. The Archbishop is, as of 2005, Monsignor Guillermo José Garlatti. Museums include the Port Museum, the History Museum, the Fine Arts Museum and the Contemporary Art Museum. There is also a zoo in the town. Areas of interest include the Barrio Inglés ('English Quarter') where the British foremen and technicians who built the railways and ports lived. Villa Harding Green is a suburb where the railway and port managers lived.

Outside the town there are beaches at Maldonado and Colón, plus resorts further away at Pehuén-Có and Monte Hermoso.

Nobel laureate Cesar Milstein was a Bahía Blanca native.

Ever since the 1950s, Bahía has been the capital of Argentine basketball, with Emanuel Ginóbili being the latest link in a long chain of famous native players. The city's main football (soccer) team, Olimpo, played in the Argentine first division until relegation in 2006. Argentina national football team coach Alfio Basile is also a bahiense.

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