The limits of Buenos Aires proper are determined in the eastern part and north-east by the Rio de la Plata, in the southern part and southeast by the Riachuelo and to the northwest, west and Southwest by Avenida General Paz, a 24 km (15 mi) long highway that separates the province of Buenos Aires from the 203 km that form the city.
The city of Buenos Aires lies in the pampa region, except for some zones like the Buenos Aires Ecological Reserve, the Boca Juniors (football) Club "sports city", Jorge Newbery Airport, the Puerto Madero neighborhood and the main port itself; these were all built on reclaimed land along the coasts of the Rio de la Plata (the world's widest river).
The region was formerly crossed by different creeks and lagoons, some of which were refilled and others tube. Among the most important creeks are Maldonado, Vega, Medrano, Cildañez and White. In 1908 many creeks were channelled and rectified, as floods were damaging the city's infrastructure. Starting in 1919, most creeks were enclosed. Notably, the Maldonado was tube in 1954, and currently runs below Juan B. Justo Avenue
