Over the last few decades more and more natural wastewater treatment systems have been built in Hungary. The present study is the first step in creating a broad database on the water quality parameters and on the pollutant removal efficiency of these systems. The investigation included 78 plants out of which we analysed 16 systems in detail. Four types of natural methods are evaluated: wetlands, ponds, biomechanical combined oxidation (BMKO) systems, and poplar plantations. Pond systems are efficient in ammonium-nitrogen (NH4-N) removal, reducing it with 83% (41-88%). Their chemical oxygen demand (COD(Cr)) removal capacity is only 55% (37-81%). The only BMKO system that could be evaluated performs high COD(Cr) (77%) and total suspended solid (TSS) (89%) removal. Removal of NH4-N and total nitrogen (TN) declines during the years of operation giving an average value of 39% and 49%, respectively. The system is not efficient in phosphorus removal (13%). In wetlands the 71% COD(Cr) (53-96%), and 57% TSS (33-91%) removal provides satisfactory effluent quality most of the time. Wetlands performed low nutrient removal, i.e., 17% (-21-46%) for TN and 26% (-20-92%) for phosphorus. Poplar plantations are very effective in pollutant removal. Even the average removal of each nutrient type is above 75%. Several problems have occurred in the operation of natural treatment systems. However, if carefully planned and constructed, and the required maintenance work is done properly, they can be possible alternatives for wastewater treatment.