Utrecht’s fish doorbell, an internet hit which has allowed tens of thousands of people all over the world to help fish migrate through the city’s canals, is online again for the sixth year.

Thousands of fish make the journey upstream in the river Vecht each spring but because the gates of the Weerdsluis lock are not opened frequently enough, the fish are faced with long waits in the city’s Oudegracht.

Via an underwater camera people who spot waiting fish can ring the bell, alerting the lock keeper. He receives screenshots of the fish and can open the doors to let them through. In 2025, the gates were opened some 200,000 times.

“Migration is vital for fish, to find food and to breed,” ecologist Marco Kraal told Nu.nl.  He said it is difficult to predict if more species will present themselves at the gates this year, and when the migration will begin. “It depends on the amount of light,” he said.

This year, Kraal is expecting the water to be less murky, which will attract more carp but will send pike and perch in search of deeper and more shadowy water. Last year, more eels were spotted than in the preceding years.

In 2025, the fish doorbell platform was visited 30 million times by 2.3 million visitors worldwide.