We are right in the middle of Fish Doorbell season—but what is that? In short, the Fish Doorbell is an underwater live stream that gives the public the ability to open a canal lock for migratory fish.

The idea for it was sparked when Anne Nijs and Mark van Heukelum noticed a build up of fish waiting at the Weerdsluis lock in Utrecht. Anne says, “…some fish species migrate to shallower water and they swim right through the center of Utrecht looking for a place to spawn and reproduce.” However, at the time of year the fish migrate, Spring, there are no boats sailing through, and thus the lock rarely opens.

Because the fish were stuck waiting, they were more susceptible to being eaten by predators. This means the fish have lower chances of surviving long enough to reproduce, posing a threat to their population.

To remedy this, Mark suggested positioning an underwater camera beside the lock. The livestream lets the public watch for fish waiting for the lock to open. When a fish is spotted, people can ring the digital doorbell to let the lock operator know—once there are enough fish in the “queue,” the operator opens the lock to give them passage.

This lessens the chances of the fish being eaten and improving the odds they’ll reproduce successfully, improving the health of the population, and in turn improving the quality of the water. The doorbell helps in other ways too, though. The livestream helps collect data on which species pass through the canal, as well as various physical attributes of the fish, such as size and gender. Public awareness is raised regarding the underwater world of the canals, and the livestream has gained attention from around the world.