The Agger is a river in Germany, a right tributary of the Sieg in North Rhine-Westphalia.

Its source is in the Sauerland hills, near Meinerzhagen.

It winds through the towns Engelskirchen, Overath and Lohmar.

Near Siegburg the Agger flows into the Sieg.

This article related to a river in North Rhine-Westphalia is a stub.