Ding Dong! In the city of Utrecht, The Netherlands, fish are calling and people all over the world are answering.

By Caroline Johnson, intern

Many species in the animal kingdom partake in spring migration this time of year, and that’s no different for the freshwater fish species of Utrecht, The Netherlands. Except here, fish must first pass through a special door opened with the help of thousands of people around the globe watching from an underwater livestream camera… Holy ‘carp’!

The city of Utrecht, the fourth largest city in The Netherlands located just 45 minutes south of Amsterdam, boasts the world’s first ever Visdeurbel, or ‘fish doorbell’ to facilitate the seasonal migration of fish populations through the city’s canals on their way to lay eggs in the shallow-water areas upstream. 

How does Visdeurbel work? 

To reach their breeding destination, fish must pass through Utrecht’s Weerdsluis boat lock, situated in a canal in the heart of the city. However, at the start of fish migration season in March, few boats sail through the canals, meaning the lock seldom opens, potentially keeping thousands of fish from their spawning journey. 

Scientists observed that as fish congregated around the lock, the site became a popular feeding ground for predators like larger fish and birds to stake out a quick and delicious meal. Fish in migratory season are already vulnerable to predatory practices, and the lock only increased the risk faced by fish.

So, in March 2021, a group of scientists and the municipality installed an underwater camera right at the entrance to the lock that broadcasts a 24-hour livestream feed to viewers all over the world. Viewers can watch the livestream any time and click a virtual doorbell button if a fish appears which signals to a lock operator that there is a fish needing to pass through and to open up the lock.

How to watch the fish doorbell in action

You can watch the livestream here. Optimal viewing times include morning or evening hours (and consider the time change if you are outside The Netherlands).

Is Visdeurbel working? 

In its first two weeks of operation four years ago, the Visdeurbel website allowed 23,000 fish to pass through the lock. In 2024, the website welcomed over 2.7 million viewers from the United States to Brazil to Australia, with the doorbell button pressed over 40,000 times.

Some of the most common fish species to pass through in 2024 include freshwater bream and perch, but the livestream also captured carp, catfish, and even eel. The doorbell system is not just for fish and benefits the crab, lobster, frog, and geese populations in the area.

Not only does Visdeurbel help aquatic species pass through the lock, the underwater camera also helps scientists collect data on the canals’ aquatic residents and record any changes from year to year. Fish populations play a crucial role in clean waterways, and monitoring their health can indicate water quality. Furthermore, Visdeurbel serves as an education tool to the people all over the world about our life below water. 

Wildlife corridors help countless species 

While migratory season for fish begins in early March, migration ramps up in April when the water gets warmer. Accordingly, the website goes live from the beginning of migratory season in early March and concludes at the end of the season in May.

In the United States and around the world, wildlife including fish, birds, tiny turtles and giant whales all migrate at different times of the year to find food and suitable places to raise their young. But as human development has expanded, many migration routes are disrupted and the remaining habitat is often fragmented, penning animals into areas too small for their survival. Wildlife corridors and crossings, like this fish passageway, help solve the problem by reconnecting habitats and helping animals get around barriers like roads and dams.

More threats to fish 

Dams aren’t the only challenge fish will face this spring. They’re also swimming up rivers increasingly polluted with plastic, including plastic pellets. These little beads of plastic are used to manufacture toys, toothbrushes, water bottles and more, but they’re frequently dumped or spilled into waterways. Microplastic is harmful to both fish and people. It can interfere with their gills, the gut and even a fish’s DNA.

So, in addition to watching Visdeurbel and reducing your own plastic use, what can we do? One simple step is to look for plastic in your own local waterways to identify problems and build support for solutions. Sign up below to join us for a plastic pellet count in your area.