The fish doorbell was created to help fish that want to lay eggs in the direction of the Kromme Rijn. Especially in early spring, when there are few boats, the lock sometimes remains closed for a long time and the fish cannot continue.
The fish doorbell is not a real doorbell, but a website where you can see live underwater images of the lock. Do you see a lot of fish? Then you can press a button and the lock keeper will receive a signal to open the lock.