Lake Ptuj is a reservoir on the Drava River, created in the 1970s by the Formin hydroelectric dam, about 3 km southeast of the old town. Despite its industrial origin it has become a pleasant recreational area: there is swimming in summer, a campsite on the shore, and good birdwatching in the surrounding wetlands.
The lake is particularly worthwhile for migratory birds in spring and autumn, with cormorants, herons, and various waterfowl using it as a stopping point. The walk or cycle ride from the old town along the Drava is straightforward and pleasant.