the fresh waters of western Europa, either current (brooks,
rivers) or still (swamps, peat-bogs, puddles, ponds, lakes), the pennate diatoms dominate.
Only about thirty species of centric diatoms are present. Most of the
species proliferate on the bottom (benthic species), either free or fixed to various mineral or organic supports. Planktonic species are present mostly in still and stagnant waters.
in puddles and ponds, three to five tens of taxa can be found, in large
lakes, until several hundredth of taxa can be present. In the Lake of
Neuchatel, 408 taxa (111 planktonic taxa and 297benthic taxa) have been collected (Wuthrich, 1960).
While most of the species of fresh waters do not support the presence of salt (stenohaline species), some ones accept a moderate salinity (euryhaline species) allowing them to be also present in brackish waters.