Guaraíras Lagoon is a shallow coastal lagoon subject to human impacts, including shrimp aquaculture, urban expansion and agricultural activities. Guaraíras is part of a complex lagoon called the “Complexo Lagunar Estuarino Nísia Floresta-Papeba-Guaraíras”, consisting of three interconnected lagoons of which Guaraíras is the largest. The lagoon is about 7 km long, and is a shallow lagoon with depths ranging from 0.5 to 2 m and up to 11 m in the narrow channels. The lagoon is part of the Rio Jacú hydrographic basin, and this river supplies the main inflow of fresh water, in the innermost part of the lagoon.
The description of the historical evolution of the morphology of the Guaraíras Lagoon reports that the system underwent successive natural changes in its dynamics, with some periods of isolation and others of connection to the sea. In 1923, a narrow canal was opened connecting the lagoon to the sea, with the objective of draining the lake during the rainy season. This canal rapidly widened, permanently linking the lake to the sea. Taking this into account, a lagoon regime was formed, with tidal action.
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Water in silled lagoons is retained at all states of the tide by a barrier
of rock (the ‘sill’). There is usually little tidal rise-and-fall.
Seawater input is regular (i.e. on most tides) and although salinity
may be seasonally variable, it is usually high, except where the level
of the sill is near to high tide level. These lagoons are restricted
to the north and west of Scotland and may occur as sedimentary basins
or in bedrock (where they are called ‘oban’). Muddy areas are
dominated by filamentous green algae, amongst which may be colonies of
rare charophytes, such as foxtail stonewort Lamprothamnium
papulosum. There may be beds of tasselweed Ruppia spp.
and, in the deeper most stable lagoons, eelgrass Zostera marina.
