The surface area of the lake is 17.9 square kilometres (6.9 sq mi).

The 167 cm cross, formerly situated on the bank of the lake, has now been exhibited in the Tver History Museum for over a century.

Lake Sterzh is oriented north to south, with one bay stretching to the east.

The lake is shared between Ostashkovsky (north) and Penovsky (south) Districts of Tver Oblast.

The drainage basin of Lake Sterzh includes the northern part of Ostashkovsky District and minor areas in the northeast of Penovsky District.