barges though the river locks at Heidelberg, Germany

An eastbound upriver barge laden with gravel approaches the locks.

The barge enters the lock.

Now joined by a pleasure craft heading in the same direction, the gates are closed behind them and the upstream gates opened.

Another barge with unknown cargo heading westbound downstream enters the lock in the other direction.

The water level having fallen to that of the downstream entrance, the gates are opened and the barge motors out. The eastbound barge has already left

Staying with Heidelberg, here is a sequence taken of barges passing through the Schleusen (locks), one in each direction, on the Neckar River, by the city. (Geoff Churchman)