It is a one-way (water) street: if your ship or boat enters the Landwehr Canal at the upper part of the canal (at the "Oberschleuse"), it must inevitably pass through to the end of the canal. To get back to the starting point, a drive through downtown Berlin is required. The minimum travel time (including the way back) when traveling through the Landwehr Canal is therefore four hours. The only exception are ships with home ports in the canal (Josi & Phillippa). Low bridges sometimes prevent large event ships from passing through. For small rental boats there is the problem of not being allowed to drive through the city center on the way back, since a radio system and the corresponding license are required here during the day.