Utrecht’s famous “fish doorbell”, monitored and rung by tens of thousands of people all over the world, is not as it seems, local broadcaster RTV Utrecht reported at the weekend. The system went online on March 2 for the sixth year.

The website and publicity for the scheme, which is supposed to help migratory fish move up river to their spawning grounds, imply that webcam watchers are alerting the lock keeper to the presence of fish so they can open the gate and let the fish swim onwards.

“Did you spot a fish? Press the Fish Doorbell!,” the English version of the website states. “Then our lock keeper can let the fish through.”

However, RTV Utrecht reported on Saturday there is no direct link between the presence of the fish and the lock opening.

Instead, a ring on the online bell generates a photograph which goes into the city council’s database and is monitored occasionally by ecologists researching fish movements.

In March, when the doorbell officially goes online, the gates are only opened a couple of times a month, whether or not fish have been spotted waiting to swim through. And it is city ecologist Mark van Heukelum who decides when to open the sluice gates, not the thousands of people watching for fish.

Van Heukelum admitted to RTV Utrecht that the public may have the wrong idea and that there is no direct link between the presence of fish on camera and opening the gates. Rather, he plans a week in advance when the sluice will open, depending on which migratory fish are to be expected – with the help of the fish photo data base.

The system was introduced in 2021 and since then millions of people have tuned in to watch for fish. “Sometimes it is so busy that every fish to appear in front of the camera is registered 30 times,” he said.

The system costs some €40,000 a year to operate, even though it serves no real purpose. “The live aspect is meant to involve people in life under water,” he told RTV Utrecht. “And to have a bit of fun at the same time.”

The fish doorbell organisation told Dutch News that RTV Utrecht had taken words out of context. “From the start we have explained how it works: FAQ — The Fish Doorbell,” the organisation said.