Lake deposition
The energy of water flow in a lake is significantly lower than that of the stream or river that feeds it. Because of this the water may no longer have enough energy to carry the sediment it is transporting; hence lakes are areas of sediment deposition. Lake deposits are termed lacustrine.
Where streams enter the lake the energy of the water drops off, so the largest particles are deposited closest to the mouth, whilst finer particles may be carried further into the lake before being deposited, this process creates fans of materials at the mouths of rivers and streams entering the lake that are grade from coarse to finer material.
As well as allocthanous material (external to the lake) transported by streams, lake sediments also include autocthanous sediments (internal to the lake) such as the remains of aquatic animals, plants and plankton, together with chemical precipitates such as calcite.
Sediment deposition in lakes can be highly seasonal reflecting flow conditions in the streams that feed them. This can create annual varves, which can provide a sensitive record of environmental change in the river catchment.