The lake is located at Nizhny Novgorod region, Russia.
The name “Vad” comes from Mordovian language and means “water”. The Vad Lake is located on the way of the Vadok river, that goes underground just before the lake. The river goes some distance underground, and then finds its way to the surface, creating a grotto at the lake’s bottom. In winter, the water does not freeze over the sinkhole. Pressure of underground water is so strong that it creates a convex lens above the surface of the lake.