Pollution tolerant protozoa in polluted wetland

•Protozoan communities of polluted wetland were identified.•Eight dominating protozoan species were proposed to be pollution tolerant species.•These species can be used as indicator for polluted waters.•The protozoa can participate in the energy transfer chain in polluted wetlands.

This study for the first time confirmed that eight dominating protozoan species, Cryptomonas erosa, Euglena axyuris, Euglena caudate, Euglena gasterosteus, Euglena acus, Vorticella campanula, Vorticella convallaria and Epistylis lacustris, were the pollution tolerant species at chemical oxygen demand 54-104 mg/L. These species cannot be used as indicator for clean water quality as commonly believed. The protozoa can be actively participating in the energy transfer chain between nano-planktonic and higher plants in polluted wetlands.