Four lakes

The water surface of the Alfsee covers 2.2 km² and its shore is about 7 km long. Its maximum north-south length is 2.88 km. From east to west the lake is up to 330 m across in the south and 1,350 m in the north. It has a capacity of 20 million m³ at a depth of 2 m.

Immediately to the south, where the artificially constructed conduit of the river Hase flows into the Alfsee lakes, there is a small auxiliary basin (Absetzbecken) in front of the actual reservoir, from which water flows into the lake via a roughly 330 m long overflow dam.

To the east the Alfsee borders on the small Dubbelausee, which is up to 400 m long in an east-west direction and up to 360 m long from north to south and set at a height of 37 m above sea level (NN).

Just to the northeast, as part of as small nature reserve there is a reserve basin (Reservebecken), which is up to 700 m long from north to south and a maximum of 425 m from east to west.

Head- and tailwaters

Roughly north of the town of Bramsche an artificial channel branches off the Hase that takes water from the south for about 4.5 km to the lakes of the Alfsee. The water draining from the Alfsee runs over a similar artificial drainage channel, about 1.3 km long, directly west of the reserve basin north of the Alfsee, where it flows along the 2.5 km long canalised lower reaches of the Ueffelner Aue, which passes the Alfsee to the west running in a south to north direction west of Alfhausen, before flowing back into the Hase.