Abstract
There are two freshwater environments which are considered to be severe conditions for the survival of living creatures. One is inorganic acid or alkaline lakes and rivers resulting naturallyfrom the inflow of acid or alkaline spas and springs. The other is artificially polluted waters by inflow of drainage from households, sewage treatment equipment and barns etc. In such environments, the existence of almost all organisms is inhibited, but diatoms are one of the group of organisms able to grow in such severe environments. Moreover, some diatom taxa occurred in large quantities in these environments. In this paper, we summarize the dominant taxon of many attached diatom assemblages occurring in severe environments from the view point of ecology.
