Ans. Desmids are usually found in freshwaters like ponds, lakes, and rivers. It is a kind of phytoplankton, which lives in the bottom as benthic dwellers of the water source. The nutritious content present in the freshwater supports the growth of desmid algae. They are also found in saline waters, snow, ice..etc. But, the polluted water does not have enough nutrients. So, it cannot support the reproduction of mixed desmid.