The article strives to determine the allowable content of nutrients in wastewater that is being discharged into a reservoir, with the end goal of minimizing the risk of eutrophication. It is noted that the methodology currently used in Ukraine and most European countries to control pollutant discharge in wastewater is designed to simply not exceed the permissible pollution level in natural water based on sanitary indicators, which does not guarantee the absence of the eutrophication risk to the water bodies. The article describes a developed method for determining the allowable composition of wastewater based on biogenic indicators. The proposed method takes into account the consecutive transformation of nutrients, the probabilistic nature of the factors that determine the quality of water in water bodies, as well as the cost of purifying wastewater from various pollutants. The problem is considered for the case of wastewater discharge into a reservoir through a watercourse. This research is a practical scientific base for further improving the methodology for standardization of the wastewater composition in order to protect water bodies from eutrophication.