Small Hydropower Plants’ Impacts on the Ecological Status Indicators of Urban Rivers

Water is the basis of life for living creatures and is used for various purposes, especially in agriculture, industry, municipal services, and energy production. Assessing water quality in terms of its various uses is not without significance. This study investigates the water quality within two small hydropower plants (SHPs) in central European urban areas from an environmental perspective. Wrocław I and Wrocław II SHPs on the Odra River in Poland were selected as case studies. This study presents the results of four-year observations (2017–2020) conducted in different locations located upstream and downstream of the barriers. The following aspects were assessed: physicochemical status, trophic status, assessment of fish living conditions, and water quality indices. The results show that SHPs improved the average physicochemical status of the five-day biochemical oxygen demand (i.e., BOD5; by 6.19% comparing the results downstream and upstream of the SHPs), dissolved oxygen (3.85%), PO4-P (3.31%), and electrical conductivity (0.52%); however, they worsened in the case of the pH (by 2.63%) and NO3-N (by 1.83%). Water near the study cases is classified as mesotrophic or eutrophic. The conditions for salmonids and cyprinids were not met due to the increased concentrations of NO2 and BOD5 values; in the case of salmonids, also due to the temperature and dissolved oxygen concentration. The water quality indices differed and indicated the quality from poor to good, depending on the classification. This study provides important insights for policymakers regarding the awareness of the impacts of SHPs on water quality in urban areas and the immediate measure needed to be considered to improve aquatic habitat conditions.