Lock 23 is one of the last locks in direction Kelheim, that still contains water. Most of the other locks have been drained or destroyed during construction of the new Main-Danube Canal.
Some of the "dry" locks are shown at the homepage of Gerhard Wilhelm. Beside others he has also made nice pages about Ludwigs Canal. He also gave me the hint, that lock number 1 in Kelheim still exists.