Lagoa Dos Patos
Lagoa dos Patos (“Lagoon of Ducks”) is the world’s largest coastal lagoon. Its name is said to have been given to it by Jesuit settlers in the 16th century, who bred waterfowl on its shores. It is a shallow, tidal body of water, 155 miles (250 km) long and up to 35 miles (56 km) wide. A sand bar separates it from the Atlantic, with which it connects at its southern end via a short, narrow channel that disgorges a large plume of sediment into the ocean. Marine animals use this channel to access the lagoon; sea turtles are found in the lagoon in spring and summer.
At its northern end, the lagoon receives an inflow of fresh water from the GuaÃba Estuary, formed from the confluence of the Rio Jacui and three smaller rivers. Along its inner side are a number of distinctive wavelike “cusps” that have been caused by the accumulation and erosion of sediments driven by tidal action and winds. The salinity of the lagoon varies. It consists mainly of fresh water at times of high rainfall, but there is considerable saltwater intrusion at its southern end at times of drought. Lagoa dos Patos is one of Brazil’s most vital fishing grounds. However, run-off from rice fields and pastureland, industrial effluents, and increasing population have led to concerns for the lagoon’s ecosystem.