How a ‘doorbell’ is helping migrating fish in the Netherlands

March 19, 2025 journo

There’s a special doorbell in the Netherlands, and not for your neighbours, but instead for migrating fish.

The City of Utrecht, about 40km south-east of Amsterdam, has installed a “fish doorbell” on a river lock that lets people watching a livestream alert authorities to fish being held up as they make their springtime migration to shallow spawning grounds.

The idea is simple: an underwater camera at Utrecht’s Weerdsluis lock sends live footage to a website.

When somebody watching the site sees a fish, they can click a button that sends a screenshot to organisers.

A perch fish underwater. — Perch fish are just one species of fish that migrate through Utrecht on their way to spawning grounds. (AP: Visdeurbel )

When they see enough fish, they alert a water worker who opens the lock to let the fish swim through.

Now in its fifth year, the site has attracted millions of viewers worldwide with its quirky mix of slow TV and ecological activism.

The screen is mostly taken up by murky sea-green and occasional bubbles, but sometimes a fish will swim past and as the water warms up, more fish show up.

A school of fish swimming around in green water. — Fish are let through the locked area when enough are spotted by the livestream viewers. (AP: Visdeurbel)

Without the help, native freshwater fish like bream, pike and bass can become backed up behind the lock and form easy prey for predators in the spring, when the lock is rarely opened for passing boats.

‘A beautiful story’

A man holding a large wheel next to a river. — A wheel is used to manually open the lock. (AP: Aleksandar Furtula)

The doorbell is the brainchild of ecologist and concept developer Mark van Heukelum.

He’s been happily surprised at the response, with millions of people from around the world tuning in over the years.

“I guess the combination of a good cause, a beautiful story and just a simple idea generates all this attention,” he said.

Anna Nijs, an ecologist with Utrecht municipality, was also amazed at the popularity of the concept around the world.

“We get a lot of fan mail from people who think it’s slow TV and they find it relaxing,” she said.

“They appreciate that they can actually do something to help.”