Lagoons are areas of shallow, coastal salt waters, wholly or partially separated from the sea by sandbanks, shingle or, less frequently, rocks. Five main sub-types of lagoon have been identified in the UK, on the basis of their physiography, as meeting the definition of the habitat type. These include, isolated lagoons, percolation lagoons, silled lagoons, sluiced lagoons and lagoonal inlets.

Coastal brackish lagoons are the only marine priority habitat type in the UK. They are pond- or lake-like bodies of saline water of restricted tidal range, either wholly or partially separated from the adjacent sea, but with some influx of sea water. They are commonly shallow, often with a varying salinity range both above and below sea water levels. They offer an unusual habitat, often temporary, and invariably under pressure from pollution. Lagoons support a characteristic community of invertebrates and submerged flora, often of low diversity, but several of which are rare and protected under the Wildlife and Countryside Act (1981).

The sensitivity of a lagoonal site varies not only on a site-by-site basis but also across different time periods. The nature of sea-water exchange is critical to the survival of the habitat, but there is limited information on the natural variability of habitat and biotic characteristics. This makes assessment of its relative sensitivity and vulnerability to human influences difficult.

The tables below summarise the potential threats to lagoons from land and waterborne processes.

Water based processes

Land based processes

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