The Utrecht fish doorbell, which has been opening doors for fish and river crayfish to continue their way to their spawning ground on demand has attracted 1.2 million visitors from across the globe in its first month this year alone.

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 facing long waits in the city’s Oudegracht.

To remedy this, Utrecht local council and the local water authorities have installed a camera live streams the goings-on underwater.

People who spot a waiting fish can ring the bell and that will alert the lock keeper. He receives screenshots of the fish and can then open the doors to let them through.

The site has been gaining in popularity since it went online in 2021 but thanks to videos on TikTok and articles in the international media, visitor numbers are now soaring.

City ecologist Mark van Heukelum, who invented the fish doorbell, said there seemed to be “no limit to the international attention”.

“It just keeps getting bigger. Last year we had 1.2 million visitors during the spawning season and we thought we’d reached our peak but now that’s what we had in the first month,” he told RTL Nieuws.

The high visitor numbers also create challenges, Van Heukelum said. On some days the bell is pressed up to a thousand times, including when no fish are waiting to get through. “We are now using automatic image recognition to quickly scan the screenshots, so we can disregard those that show nothing.”

The fish doorbell can be rung until the end of May or thereabouts.