Stever Inflow into Hullern Reservoir

Reservoirs also need inflows.
Wikipedia:
The Hullern dam (Hullerner See) in the Recklinghausen district in North Rhine-Westphalia dams the Stever above the Haltern reservoir. Gelsenwasser AG uses the dam to produce water and it is also used for quiet relaxation. The dam was inaugurated on October 15, 1985 after thirteen years of construction.

The water depth is a maximum of eight meters.

The Hullern rubber weir acts as a fore-dam and ensures a consistent water level in the upper reaches of the Stever when the water level in the Hullern dam is lowered. It ensures that the water level in the river does not fall too far, even if the reservoir level in the dam is lowered for water management reasons. When the water level in the lake is lowered, the water from the Stever flows into the reservoir via a fixed ramp.
gelsenwasser-blog.de/die-wehre-im-talsperrensystem-haltern-und-hullern