It's that time of year again – the Fish Doorbell season has begun. For several years now this innovative project in the small Dutch city of Utrecht has been causing a splash. But what exactly is it?
In short, the Fish Doorbell is a system designed to help fish migrate through canals. A camera near Weerdsluis lock streams live footage, allowing the public to spot waiting fish. When enough fish are seen, viewers can press a virtual doorbell, alerting lock operators to open the gate.
How did the Fish Doorbell begin?
Four years ago, two ecologists – Anne Nijs and Mark van Heukelum – were standing beside the lock looking at some artwork when they noticed lots of fish in the water. Lots of big perches were waiting for the lock to open.
“In the early spring, when the water gets warmer, some fish species migrate to shallower water and they swim right through the centre of Utrecht looking for a place to spawn and reproduce,” says Anne. But at this time of year “there are no boats sailing through Utrecht so the lock rarely opens.”
While they’re stuck waiting around for the lock to open, the fish are left vulnerable – if predators realise they’re loitering, they could come to snap them up. The lock should open more often in spring to let the fish go on their way, they thought, but how would the lock operator know if fish were waiting to go through?
What is the Fish Doorbell?
Mark came up with the idea of the Fish Doorbell. A live stream in the water lets members of the public keep an eye out for fish gathering by the gates. When they see them waiting, they ring the digital doorbell to alert the lock keeper that fish are waiting.
When there are enough fish in the 'queue', the keeper opens the wooden gates so the fish can continue their journey more quickly and with less chance of being eaten.
“But with the underwater camera and all the screenshots and videos, we also do monitoring so we know what fish species we have in the canal and when they arrive,” says Anne.
This helps them learn which species pass through, what time of year and day they swim by, their size, gender and any changes compared with previous years.
As well as freshwater bream, common roach, crabs and walleye, they’ve spotted some unusual species, such as eels – which travel in the opposite direction, says Anne: “The only place the eel reproduces is in the Sargasso Sea, 5,000 km away from the Netherlands.”
Last year, the response from the public was huge with people logging on from all over the world, including England, America, Australia and New Zealand.
“Some people are obsessed by it and we receive a lot of fan mail,” says Anne. In 2024, the website had 9.3 million visits in total and the fish doorbell was rung over 40,000 times.
As well as helping the fish migrate so they can complete their life cycle, the Fish Doorbell also plays an important role in education, says Anne: “The underwater world is a hidden world and we’ve noticed that the fish doorbell opens the eyes of many who did not know about the fish that live here and why they need our help.”
Main image: Fish Doorbell/Visdeurbel
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