“In the early spring, when the water gets warmer, some fish species migrate to shallower water, and they swim right through the center of Utrecht looking for a place to spawn and reproduce,” ecologist Anne Nijs tells
BBC Wildlife’s Melissa Hobson.
But the lock cuts off the
animals’ progress—and waiting near it puts fish in a life-threatening position. When fish are stuck in the canal, predators like
grebes and
cormorants can more easily snatch them.
To help fish migrate safely during the canal’s quiet season, Nijs and van Heukelum came up with an innovative solution:
the fish doorbell (or
de Visdeurbel in Dutch). Launched in spring 2021, the webpage features a live stream from an underwater camera, allowing viewers worldwide to check for fish waiting at the closed lock—then, they click a pink button on the site when the animals appear on screen.
Each time a user “rings” the doorbell, the service snaps a picture of the fish and sends it to a team of ecologists. After enough fish are waiting, they notify the lock’s operator that the gate should be opened.