The Irregular Contours of Lagoa Mirim, Brazil
Lagoa Mirim (Portuguese) or Laguna Merín (Spanish) is a large estuarine lagoon which extends from southern Rio Grande do Sul state in Brazil into eastern Uruguay.
Like its larger neighbor Lagoa dos Patos to the north, Lagoa Mirim is separated from the Atlantic Ocean (lower right) by a sandy, partially barren peninsula.
The Lagoa Mirim is about 108 miles (174 km) long by 6 to 22 miles (35 km) wide. As evidenced by the radar (ASAR) image, the lake has a very irregular outline (more so than that of Lagoa dos Patos). It discharges into Lagoa dos Patos through the navigable São Gonçalo Channel.
The Lagoa Mirim has no direct connection to the Atlantic, but the Rio Grande, a tidal channel about 24 miles (39 km) long which connects Lagoa dos Patos to the Atlantic, affords an entrance to the navigable inland waters of both lagoons and several ports.
The southern part of the lake lies in Uruguayan territory, but its navigation, as determined by treaty, belongs exclusively to Brazil.
Both of these lakes are evidently the remains of an ancient depression in the coastline shut in by sand beaches built up by the combined action of wind and current.
They are of the same level as the ocean, but their waters are affected by the tides and are brackish only a short distance above the Rio Grande outlet.
The Jaguarão/Yagurarón River, which forms part of the boundary line with Uruguay, empties into Lagoa Mirim, and is navigable 26 miles (42 km) up to and beyond the town of Jaguarão.