The Riga Hydroelectric Power Plant was put into operation in 1974. In order to build Riga HES, a dam was constructed across the Daugava River through the middle of Doles Sala, half of which has since been flooded to make room for Riga Reservoir. Along with Doles Sala, several other smaller islands also drowned when the reservoir was filled. The dam was built in the late 1970s. Aside from its main purpose of keeping the reservoir contained, its top is used as a motor vehicle highway. A railroad was also const