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Lagoa dos Patos
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Lagoa dos Patos (Portuguese pronunciation: [laˈɡoɐ dus ˈpatus]; English: Ducks' Lagoon) is a coastal lagoon located in the state of Rio Grande do Sul, southern Brazil. It covers an area of 10,100 km2 (3,900 sq mi),[2] is 290 kilometres (180 mi) long and has a maximum width of 71 kilometres (44 mi).[4] It is the largest choked coastal lagoon in the world,[5] the largest coastal lagoon in South America, and the largest lagoon in Brazil.[2]
Key Information
Lagoa dos Patos is separated from the Atlantic Ocean by a sandbar about 8.0 kilometres (5 mi) wide. The Jacuí-Guaíba and Camaquã Rivers empty into it, while the navigable São Gonçalo Channel, which enters Lagoa dos Patos near the town of Pelotas, connects Lagoa dos Patos to Lagoa Mirim to the south.[2] The Rio Grande, at the south end of Lagoa dos Patos, forms the outlet to the Atlantic.[2]
This lagoon is evidently the remains of an ancient depression in the coastline shut in by sand bars built up by the combined action of wind and current. The shallow lagoon is located at sea level and its waters are affected by the tides, normally they are brackish only a short distance above the Rio Grande outlet,[2] but this can vary a lot. In droughts and favorable winds, sea water can be carried up to almost the entire lagoon.[6]
The lagoon's largest and most fertile island is the Ilha dos Marinheiros, which is located near the eastern shore. The island is geopolitically part of the municipality of Rio Grande.[citation needed]
The lagoon hosts a rich biodiversity, including fresh- and brackish water fish, and water birds such as black-necked swan, coscoroba swan and Chilean flamingo.[2] Top predators from ocean ecosystem, notably common bottlenose dolphins, can sometimes be seen at Lagoa dos Patos[7][8] and exceptionally southern right whales are found at the Rio Grande outlet.[9][10]
Geography
[edit]The lagoon has average length and width of 290 km (180 mi) and 40 km (25 mi), respectively. It covers a surface of 10,100 km2 (3,900 sq mi),[2] slightly smaller than Jamaica, and occupies nearly one third the area of the Coastal Plain of the state of Rio Grande do Sul. The lagoon roughly runs NE-SW, with an average depth of almost 6 m (20 ft), and mean tidal amplitude of 0.45 m. At its southern end, near Rio Grande city, the only inlet of Lagoa dos Patos has a mean discharge of 4,800 m3/s (170,000 cu ft/s). Sea water penetrates northwards into the lagoon up to 200 km during exceptional conditions favored by southern winds, low water levels in the lagoon, and spring tides. The lagoon receives freshwater from about 201,626 km2 (77,848 sq mi),[1] mostly from the catchment basin of the Guaíba River system, whose mouth is located in Porto Alegre - the Jacuí Delta - at the northwestern end of the lagoon. The coastal plain bordering the lagoon typically has elevations that reach up to 6 m, mostly consisting of sandy deposits interrupted by small inlets. Those spits rise in average 1 m above the mean water level and on the west margin of the lagoon their submerged part extends about 15 km into the water body.[3]
Tributaries
[edit]Major tributaries of the Lagoa dos Patos basin:[11]
Towns and cities on coast
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References
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Wikimedia Commons has media related to Lagoa dos Patos.
- ^ a b c U., Seeliger (2001). The Patos Lagoon Estuary, Brazil.
- ^ a b c d e f g h "Laguna dos Patos". Freshwater Ecoregions of the World. Archived from the original on 9 January 2017. Retrieved 8 January 2017.
- ^ a b Elírio Ernestino, Toldo Jr.; Luiz Emílio Sá, Brito De Almeida; Iran Carlos, Stalliviere Corrêa; Everaldo Rigelo, Ferreira; Nelson Luiz, Sambaqui Gruber. WAVE PREDICTION ALONG LAGOA DO PATOS COASTLINE, SOUTHERN BRAZIL.
- ^ "Patos Lagoon | Saltwater, Migratory Birds, Wetlands". Britannica. Retrieved 2024-01-08.
- ^ Kjerfve, Björn (1986). "Comparative oceanography of coastal lagoons". Estuarine Variability. Elsevier. p. 63–81. doi:10.1016/b978-0-12-761890-6.50009-5. ISBN 978-0-12-761890-6.
- ^ Santos, Héric (2018). "Movimentação de água salobra na laguna dos Patos/RS mediante a utilização de imagens MODIS". guaiaca.ufpel.edu.br (in Brazilian Portuguese). Retrieved 2024-01-08.
- ^ "Projeto Botos da Lagoa dos Patos". Archived from the original on 2016-01-09. Retrieved 2016-01-23.
- ^ "Projeto de universidade monitora golfinhos em Rio Grande, no RS". 26 April 2013.
- ^ "Baleias se perdem e param na Lagoa dos Patos, no Rio Grande do Sul". 11 September 2014.
- ^ "Jornal Agora | Baleias aparecem no canal de acesso ao porto". Archived from the original on 2016-01-30. Retrieved 2016-01-23.
- ^ "Atlantic East Coastal". riversnetwork.org.
Lagoa dos Patos
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Geography
Location and Extent
Lagoa dos Patos is situated in the state of Rio Grande do Sul in southern Brazil, encompassing latitudes from approximately 30° to 32° S and longitudes from 50° to 52° W, with central coordinates around 31°06′S 51°15′W.[7][8] This positioning places it within a subtropical coastal region, forming part of the larger Patos-Mirim lagoon system that influences regional hydrology and sediment dynamics. The lagoon's extent reflects its role as a significant estuarine feature in the Pampa biome, bordered by coastal plains and lowlands.[9] The lagoon measures approximately 250 km in length from north to south, with an average width of 40 km and a maximum width reaching 71 km, covering a surface area between 10,100 and 10,360 km² depending on water levels and seasonal variations.[9][10] Its northern boundary lies near Porto Alegre, where the Guaíba River system provides primary freshwater inflow, while the southern end connects to Lagoa Mirim through the 28-km-long São Gonçalo Channel, allowing limited exchange between the two lagoons. To the east, the lagoon is separated from the Atlantic Ocean by a narrow sandbar roughly 8 km wide, which restricts tidal intrusion and defines its choked morphology.[11][12] The catchment area draining into Lagoa dos Patos spans 201,626 km², integrating multiple river basins including the Jacuí, Taquari, and Camaquã, which contribute to its freshwater dominance despite coastal influences.[10][13] Classified as the world's largest choked coastal lagoon, it exemplifies a system where a restricted inlet limits marine connectivity, and it holds the distinction of being the largest lagoon in South America by surface area.[9][14] This scale underscores its importance in regional water storage and coastal barrier formation.Physical Characteristics
Lagoa dos Patos originated during the Holocene epoch as a result of post-glacial sea-level rise following the Last Glacial Maximum, which drowned incised river valleys and fluvial systems across the coastal plain of southern Brazil. This transgression, peaking around 5,100 years before present with sea levels 2–3 meters above current levels, flooded antecedent topography and facilitated the development of sandy barrier islands and spits that progressively enclosed the basin, forming a classic choked lagoon system characterized by a single, restricted tidal inlet at the southern end. The lagoon's modern configuration emerged from the coalescence of estuarine infills in these valleys during the late Holocene, with barrier formation controlled by paleotopographic highs that guided sediment deposition and shoreline progradation.[15][16] The lagoon exhibits a shallow depth profile, with an average depth of approximately 5 meters across its expansive basin, though shallow areas less than 5 meters deep predominate in marginal zones, while deeper navigational and estuarine channels reach 10–15 meters or more in the southern sector.[10] This bathymetric variation reflects the interplay of fluvial erosion, sediment infilling, and limited tidal scouring, creating a low-energy environment conducive to fine-grained deposition in central basins. Sediment composition is predominantly sandy along the margins and in high-energy nearshore areas, transitioning to muddy substrates of silt and clay in deeper, calmer central regions, where fine particles settle due to reduced currents. These sediments are primarily supplied by fluvial inputs from the extensive drainage basin, which deliver terrigenous clays and silts during high-discharge events, while tidal currents at the inlet redistribute coarser sands and facilitate limited exchange with adjacent coastal sediments.[17][18] The physical form of Lagoa dos Patos is further shaped by its subtropical humid climate, featuring annual rainfall of 1,200–1,500 millimeters that varies interannually due to cold frontal systems and influences evaporation rates, thereby establishing salinity gradients from fresher northern reaches to more marine-influenced southern areas. This precipitation regime enhances fluvial sediment delivery while promoting seasonal water level fluctuations that affect substrate stability. The enclosing coastal barrier, including dynamic sandbars such as those associated with Ilha dos Patos features, acts as a semi-permeable boundary prone to erosion during storms and accretion through longshore sediment transport, maintaining the lagoon's isolation from the Atlantic while allowing episodic inlet breaching.[11][19]Hydrology
Tributaries and Drainage
The drainage basin of Lagoa dos Patos spans approximately 200,000 km², encompassing the pampas grasslands and plateaus of southern Brazil, where rivers collect precipitation and funnel freshwater southward into the lagoon.[20] This vast catchment integrates runoff from diverse terrains, including rolling hills and floodplains, supporting a predominantly freshwater regime despite the lagoon's coastal position. The primary tributaries are the Jacuí-Guaíba system and the Camaquã River, which together provide the bulk of the inflow. The Jacuí-Guaíba system, with the Jacuí River extending 723 km, delivers an average discharge of around 2,000 m³/s, peaking higher during floods and playing a dominant role in sediment and nutrient transport to the lagoon.[21] The Camaquã River, measuring 430 km in length, contributes an average discharge of approximately 307 m³/s, draining central pampas areas and adding significant volume from its 16,800 km² sub-basin.[22] Secondary inflows include the Sinos, Gravataí, and São Gonçalo rivers (or channel), which supplement the main system with localized drainage. These rivers vary in scale but collectively enhance the lagoon's hydrological balance, with the São Gonçalo Channel serving as a key connector from the adjacent Mirim Lagoon system. The following table summarizes the major tributaries, including lengths and mean discharges where documented:| Tributary | Length (km) | Mean Discharge (m³/s) |
|---|---|---|
| Jacuí-Guaíba system | 723 | 2,000 |
| Camaquã River | 430 | 307 |
| Sinos River | 182 | 98 |
| Gravataí River | 39 | 5 |
| São Gonçalo Channel | 76 | 700 |