Flads and gloe lakes are different stages in the process where a bay in the sea turns into a

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

due to post-glacial rebound.

Location

Flads and gloe lakes exist in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

and

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. These types of brackish lagoon are typical of the flat land of the Finnish part of the

Kvarken Archipelago Kvarken ( sv, Kvarken, Norra Kvarken (as opposed to South Kvarken); ) is the narrow region of the Gulf of Bothnia separating the Bothnian Bay (the inner part of the gulf) from the Bothnian Sea. The distance from the Swedish mainland to the Fin ...

. The island of Halsön, Korsnäs, in the Kvarken Archipelago of Finland includes a protected nature reserve covering an important area of flads and gloe lakes.

Development process

The process can be divided into four stages, and starts with a bay with some kind of threshold sill or band of vegetation that slows the influx of water from the sea. As the land rises the threshold becomes shallower and the inflow of sea water slower. In the stage called a flad, the bay is still in continuous contact with the sea, but the influx of sea water is very slow and the impact of fresh water becomes more important. Often reeds and other water plants make the influx of sea water even slower. In its natural state a flad functions as a refugium for species of the order Charales that are seemingly endangered in more open waters. At this stage human beings often interfere by dredging the threshold or cutting down reeds to prevent the bay from becoming a flad. When the flad has definitely been cut off from the sea, i.e. the threshold has risen above sea level, a gloe has been formed. Sea water still enters the gloe at high tide or when storms create big enough waves. The vegetation gets scarcer in the gloe at this stage. Finally a gloe lake has been formed when the gloe no longer has any contact with the sea and doesn't get any influx of sea water. The gloe has turned into a freshwater lake.

References

{{portalbar, Lakes Lakes by type Baltic Sea