According to this news article from the guardian about the fish doorbell the water is around 2.1m/7ft deep. Apparently the camera is at the bottom of the lock so around that depth I guess

https://www.theguardian.com/tv-and-radio/2023/jun/29/fish-do...

Also a short Youtube video from the city of Utrecht shows the whole operation https://www.youtube.com/watch?v=0MgeR85IMOM