Testerep arose around the 5th and 6th century in front of the Belgian North Sea coast between Nieuwpoort and Bredene, as a result of tidal forces.
The headland, commonly called "Ter Streep", was separated from the mainland by the Testerepvliet, a southernly situated tidal channel that was completely inundated at high tide.
Thousands of townspeople were forced to leave the original city and founded a second Ostend five hundred meters inland, no longer on the former island of Testerep but on land in the Bredene district.
In the 15th and 16th centuries, the devastating tidal waves of a new series of storm surges would eventually sink the northern half of Testerep into the North Sea.
During the reclamation of the newly silted channel lands, the Testerepvliet was canalized into the "Groot Geleed", a still existing drainage ditch north of the Moere-Blote- en Moere-Nieuwlandpolder.