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

Freshwater

Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 due to post-glacial rebound

Post-glacial rebound

Post-glacial rebound is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy...

. Flads and gloe lakes exist in the Baltic Sea

Baltic Sea

The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

 in Finland

Finland

Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

 and Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

.

The process can be divided into four stages:

Preliminary stage

In order for the process towards a gloe lake to start, a bay with some kind threshold or similar that makes the influx of water with the sea slower, is needed. As the land rises the threshold becomes shallower and the inflow of sea water slower.

Flad

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 reed

Reed (plant)

Reed is a generic polyphyletic botanical term used to describe numerous tall, grass-like plants of wet places, which are the namesake vegetation of reed beds...

 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

Charales

Charales is an order of pondweeds, freshwater algae in the division Charophyta. They are green plants believed to be the closest relatives of the green land plants. Linnaeus established the genus Chara in 1753.-Description:...

that are seemingly endangered in more open waters. At this stage human beings often interfere by dredging the threshold or cutting down reed to stop the bay becoming a flad.

Gloe

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 enter the gloe at high tide or when storms create big enough waves. The vegetation gets more scarce in the gloe at this stage.

Gloe lake

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.