Lake Ptuj (Slovene: Ptujsko jezero) is an artificial lake on the river Drava to the south east of the town of Ptuj in eastern Slovenia. It is the largest artificial lake in Slovenia and was created in 1978 when a dam for the Formin hydroelectric power plant was built on the Drava. It is still used as the reservoir for the power plant, but is also popular for rowing, sailing and fishing.