Fish doorbell

A fish doorbell (Dutch: visdeurbel) is a system that allows fish to pass through a closed sluice gate through crowdsourced input when fish are present. The Utrecht Visdeurbel uses a livestreamed underwater camera that allows users to press a doorbell button to notify the lock operator that there are fish swimming in the gracht, and that the lock should be opened. It is designed to aid in seasonal fish migration, as an alternative to a physical fish ladder. The purpose of the project is to increase the survival of local fish that are otherwise vulnerable to predation during migration.

Usage
It was deployed for the first time in Utrecht in March 2021,   at the Weerdsluis on the Oudegracht. In the first two weeks, it was used 23,000 times. It was disabled in June, but was reinstated at https://visdeurbel.nl. It ceased operation on July 1st, 2024 due to concluded migratory patterns and states an expected return date of March 3rd, 2025.