foray into the okertalsperre in northern harz in the state of lower saxony

okertal lock water level oker resin north harz low mountain range summer summery picture day trip local recreation dam building lower saxony germany europe nice peaceful important drinking landscape format outdoors district goslar central dreamy hydroelectric power station hydropower climate change altenau leisure vacation tourism travel excursion destination reserve reservoir generation electricity arched wall protection area arch weight round flood waterworks views okertalsperre state different foray into northern