moreover annual runoff may decrease due to increased evaporation in large lakes possibilities of heavy rain floods even in summer time may increase especially in small river systems flooding can cause overflows in treatment plants or problems with water abstraction affecting also water quality groundwater level may increase in winter and decline in summer reduced groundwater recharge may cause oxygen depletion in small groundwater bodies and consequently increased metal concentrations in groundwater eg iron manganese the river originates in finland and its final recipient in the baltic sea basin is lake ladoga in the russian federation