Mere (lake)

The Indo-European root *mori gave also birth to similar words in other European languages: Latin mare, ″sea″ (Italian mare, Spanish mar, French mer); Old Celtic *mori, ″sea″ (Gaulish mori-, more, Irish muir, Welsh môr, Breton mor); and Old Slavic morje.

In these circumstances, the lime (typically calcium carbonate) is deposited on the peaty bed and inhibits plant growth, therefore, peat formation.

Even quite shallow lake water can develop a thermocline in the short term but where there is a moderately windy climate, the circulation caused by wind drift is sufficient to break this up.

(The surface is blown down-wind in a seiche and a return current passes either near the bottom or just above the thermocline if that is present at a sufficient depth.)

This means that the bed of the shallow mere is aerated and bottom-feeding fish and wildfowl can survive, providing a livelihood for people around.

However, there is a limiting depth beyond which a lake does not behave as a mere since the sun does not warm the deeper water and the wind does not mix it.

Here, a thermocline develops but where the limiting dimensions lie is influenced by the sunniness and windiness of the site and the murkiness of the water.

When the Zuiderzee was enclosed by a dam and its saltwater became fresh, it changed its status from a sea (zee) to being known as the IJsselmeer, the lake into which the River IJssel flows.