The Ollenbäke has its source near the county road 346 near Langebrügge in the municipality of Bad Zwischenahn. From here it flows in a southwesterly direction. Between Bad Zwischenahn and Westerstede-Ocholt it changes its course to a northwesterly direction and flows south of Apen into the Große Süderbäke, which shortly afterwards forms the Aper Tief at the confluence with the Große Norderbäke. The Ollenbäke is influenced by the tides up to just above the municipal border between Apen and Westerstede. The tidal range is up to half a meter.
The Ollenbäke has been mostly straightened along its entire course and has been embanked on the last 750 meters above the mouth of the Große Süderbäke since the mid-1950s. It flows through areas that are intensively used for agriculture, and only occasionally through small forest areas. At Ocholt-Howiek, an old arm, the Alte Ollenbäke, branches off from the Ollenbäke. The Howieker water mill, which was built in 1608 with the permission of Count Anton Günther, is located on this river. The mill, which could only be used in winter because that was the only time there was enough water, was shut down in 1909 because the neighboring meadows suffered from the damming of the water.