Fen
In time, the lake can become so shallow that the shoreline vegetation expands into the shallow water. The lake has now become a marsh, in this early stage called a "fen". What characterizes a fen is that it still gets most of its water from the surrounding area.
Peat
There is plenty of water in a fen and it often overflows. The water is lacking in oxygen, and bacterial decay of plants and animals is incomplete. This results in the accumulation of plant remains in a thick layer that is called peat.
Peat bog
There is plenty of water in a fen and it often overflows. The water is lacking in oxygen, and bacterial decay of plants and animals is incomplete. This results in the accumulation of plant remains in a thick layer that is called peat.
The only addition of water comes from rain or snow that falls directly on the surface. This type of marsh is called a "bog". Rainwater is acidic and poor in nutrients. The vegetation becomes sparse and consists mainly of peat moss.
