Lagoa dos Patos (; English: Ducks' Lagoon) is a coastal lagoon located in the state of Rio Grande do Sul, southern Brazil. It covers an area of 10100 km2, is 180 mi long and has a maximum width of 44 mi.It is the largest choked coastal lagoon in the world,the largest coastal lagoon in South America, and the largest lagoon in Brazil.

Lagoa dos Patos is separated from the Atlantic Ocean