Coordinates: 32°00′S 52°09′W / 32.000°S 52.150°W
Ilha dos Marinheiros (Portuguese pronunciation: [ˈiʎɐ duz maɾiˈɲejɾus] "Island of the Sailors") is an island located in the south part of a lagoon named Lagoa dos Patos, located in the municipality of Rio Grande, in the state of Rio Grande do Sul, Brazil. It is situated on the west bank of that lagoon. This island has an area 39.28 km² (15.17 sq mi) and is situated 1.5 km (0.93 mi) off the continent at its nearest point.
It has 1,324 inhabitants (2000 Census), the majority of Portuguese descent.
Ilha dos Marinheiros is considered part of the heritage of the city of Rio Grande due to the preservation of the culture of the Portuguese, who colonized it. Before the arrival of the first Portuguese settlers, the island was occupied by indigenous people. According to archaeological evidence discovered there, the groups were: Minuane, Charrua and Guaraní.
The importance of the island was tied to the Rio Grande, which supplied water, firewood, and wood for the fortifications as well as for the settlers of the Town of Rio Grande de São Pedro. In the past, the island supplied all of the trade in Rio Grande and nearby locations; it currently produces about 80% of the vegetables consumed in Rio Grande.