Tasked with helping ensure Utrecht's canals remain full of life, and convincing everyone it wasn't an April Fools' Day joke, two ecologists in the Dutch city have invented the world's first "fish doorbell."

An underwater, live-streaming camera at the "Weerdsluis" lock door allows residents to ring a virtual doorbell heard by the local lock keeper when they see that fish are trying to get through.

A lock is a gate that raises or lowers canal boats into different levels of water separated by two doors, and a sluice is a small fish-sized door that allows water (and fish) to pass between them.

"You have to see the Oudegracht (the canal) as a motorway for fishing. Sometimes you see literally dozens of fish floundering in front of the lock gate, so a fish jam is created," says underwater nature expert Mark van Heukelum.

"The Weerdsluis is the link between the Vecht and the Kromme Rijn. In winter the fish swim deeper, it is warmer and safer there. In the summer they want to go to shallow water so that they can reproduce," he adds, according to AD.

Van Heukelum came up with the doorbell idea when-while working with wildlife ecologist Anne Nijs on a project to highlight the biodiversity in Utrecht's canals-they noticed how lock keeper Patrick opened the sluice to allow a large group of arriving fish to pass through.

Nijs says it's a great way to connect residents with their aquatic neighbors, and noted that when Mark took the idea to the municipality they were very excited. The only uncertainty was why create a camera and a signal to Patrick when they could just install a motion-activated sensor?

Van Heukelum explains: "Technically that is probably possible, but this is of course much more fun," he says. "I am already addicted to it myself and watch it every night. You suddenly see a large pike swimming by or a lobster. It would be nice if you could spot a rarer fish such as a bindweed or bleak. Or maybe an eel."

If you want to get addicted to watching fish swim in a Netherlands canal, you can watch the livestream here.

WATCH a video to see the doorbell in action. (See an English translation below.)

Every spring thousands of fishes swim straight through the city of Utrecht. They go through the Oudegracht in search of a spot to lay eggs. They mainly do this in the dark. Other animals can't see them at that time of day, so it is safer.

There is just one problem: the Weerdsluis doesn't open often enough… We have thought of a solution. The fish doorbell!

There is an underwater camera near the Weerdsluis. You can watch the footage live at www.visdeurbel.nl. Do you see fish? Ring the fish doorbell. The lock-keeper gets a sign. If there are many fish lying in wait, he will open the gate.

Will you help fish get through the Oudegracht? Visit visdeurbel.nl (Translated by Lara Dekker)

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