Ringing This Bell Lets Real Fishes Pass Through a Dutch Canal: How to Ring It from Around the World

Thousands are watching the livestream. In school classrooms at lunchtime, students are glued to their tablets and laptop screens, in what looks like a murky version of Pokemon Go, in which the player navigates different locations to track monsters. On one side of their screens is a tab playing the live footage. On the other side is a purple-pink button with a bell symbol. When people spot a fish passing through the livestream, they press this button. A notification pops up with dozens of cute fish doodles: Bleak, catfish, roach, eel, bream, pike, perch, and more.

Some viewers submit their own snapshots, displaying cute, curious, elusive fish travelling through the murky green waters, totally unaware of the surveillance that humans are doing to help them make babies. In the heart of the Dutch city of Utrecht, the ring of this bell alerts a lockkeeper who opens the door for the fish waiting below. The Fish Doorbell, or Visdeurbel in Dutch, operates from early March till late May, the period when fish are most active in reproduction.  

Every year in spring, thousands of fish traverse the meandering waterways of the Netherlands, swimming through Utrecht’s canals, searching for a place to spawn and reproduce. It’s the time when waters start to go warm. The river canal in Utrecht is sheltered by a lock intended to raise and lower watercrafts passing by. At this time of the year, ships are sparse, which means the locks remain closed.

The closed lock poses obstacles in the path of the fish. If the lock is opened in time, the fish become trapped in the water, getting late in reaching their destination. Stuck there, they are unable to reach the spawning grounds to lay eggs under favorable conditions. Others are picked off by predators roaming around, like grebes and cormorants.

The Fish Doorbell project was launched four years ago by two ecologists who brainstormed the idea during a complete coincidence. Anne Nijs and Mark van Heukelum were standing beside the lock, looking at an artwork when their eyes fell upon a school of fish waiting in the water. Lots of big perches were waiting on the spot for the lock to open. Propelled by the desire to help the migrating fish, they rolled out this initiative. The project, Nijs said, is a “good mix of doing something for nature and for people to join and do something,” per Scientific American.

At the time of starting, the organizers taped flyers on the streets, fearful that nobody would join. But lots of people did, exceeding their greatest expectation. In 2025 alone, millions showed up to watch the livestream. Those who were skeptical are now obsessed with the Fish Doorbell, Nijs told BBC Wildlife. “Some people are obsessed by it, and we receive a lot of fan mail.” One person suffering from depression even reached out to her and said the doorbell is the only thing that helps them feel calm and distract from difficult thoughts. Nijs said being able to ring the doorbell fills people with a “positive feeling.”

In conversation with NL Times, the doorbell’s organizers revealed that most fish are active during dawn or dusk. If you wish to spot eels or zanders, the best time to head to the livestream is at night.

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