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It might sound fishy but the world's first fish doorbell is back for another season!

The underwater camera was first set up four years ago to help the different fish species that swim in the canals of the Dutch city of Utrecht. and it streams video to a special website

Internet users who spot any fish waiting at the lock gate can ring a 'digital doorbell' to help the marine life carry on their journey,

But why do fish need the doorbell? Keep reading to find out!

Why do fish need a doorbell?

Every spring, fish swim upstream around the Dutch city of Utrecht looking for a place to lay eggs.

However, the Netherlands is a country with lots of canals and waterways and, in spring, the lock gates along these canals aren't opened much, which can make it difficult for fish to travel to their breeding grounds.

That's why four years ago experts came up with a plan to help the aquatic animals - a digital fish doorbell!

An underwater camera was installed at the lock which is live-streamed to a website which people can watch anytime of day.

As soon as they spot a fish, viewers can press a digital doorbell on the website to let the lockkeepers know when to open the gates and let the fish through - helping the fish to continue on their route!

The keeper checks if there are enough fish there to open the gates and the fish can swim on their merry way.

Researchers say that the best time to see the fish is either in the morning or at dusk - when they are at their most active.

Perch and bream were the most common fish spotted last year - but other species including catfish, pike and even eels were also caught on camera!