Brackish water

Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it can be damaging to the environment (see article on shrimp farms).

The town of Teddington a few miles west of London marks the boundary between the tidal and non-tidal parts of the Thames, although it is still considered a freshwater river about as far east as Battersea insofar as the average salinity is very low and the fish fauna consists predominantly of freshwater species such as roach, dace, carp, perch, and pike.

Like estuaries, mangrove swamps are extremely important breeding grounds for many fish, with species such as snappers, halfbeaks, and tarpon spawning or maturing among them.

Mangroves represent important nesting sites for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, shorebirds and seabirds.

Although often plagued with mosquitoes and other insects that make them unpleasant for humans, mangrove swamps are very important buffer zones between land and sea, and are a natural defense against hurricane and tsunami damage in particular.

Originally the Eridanos river system prior to the Pleistocene, since then it has been flooded by the North Sea but still receives so much freshwater from the adjacent lands that the water is brackish.

Limited mixing occurs because of the lack of tides and storms, with the result that the fish fauna at the surface is freshwater in composition while that lower down is more marine.

Hudson Bay is a brackish marginal sea of the Arctic Ocean, it remains brackish due its limited connections to the open ocean, very high levels freshwater surface runoff input from the large Hudson Bay drainage basin, and low rate of evaporation due to being completely covered in ice for over half the year.

The reservoir was created by the damming of the Red River of the South, which (along with several of its tributaries) receives large amounts of salt from natural seepage from buried deposits in the upstream region.

The salinity is high enough that striped bass, a fish normally found only in salt water, has self-sustaining populations in the lake.