The Ollenbäke has its origins near the district road 346 near Langebrügge in the municipality of Bad Zwischenahn. From here it runs in a southwesterly direction. Between Bad Zwischenahn and Westerstede-Ocholt it changes its course in a northwesterly direction and flows south of Apen into the Große Süderbäke, which a little later forms the Aper Tief at the confluence with the Große Norderbäke. The Ollenbäke is influenced by the tide up to a little above the municipal border between Apen and Westerstede. The tidal range is up to half a meter.
The Ollenbäke is mostly straightened along its entire course and has been diked over the last 750 meters above the mouth of the Große Süderbäke since the mid-1950s. It flows through intensively used agricultural areas, and only occasionally through small forest areas. At Ocholt-Howiek an oxbow lake, the Alte Ollenbäke, branches off from the Ollenbäke. The Howieker watermill is located next to it, which was built in 1608 on the approval of Count Anton Günther. The mill, which could only be used in winter because that was when there was enough water, was shut down in 1909 because the neighboring meadows suffered as a result of damming the water.