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. (C) 2017 Elsevier Ltd. All rights reserved.