The famous 'fish doorbell' is back - here's how you can help fish in the Netherlands from home

The famous Dutch 'fish doorbell' is now live, a fantastic opportunity for nature lovers across the world to help fish on their annual migration.

Every spring, fish in the Netherlands migrate upstream in search of places to spawn. Many different species swim through the tree-lined canals criss-crossing the medieval city of Utrecht, but unfortunately, the city's Weerdsluis boat lock - one of the busiest routes - is usually closed during the spring.

In years past, a lockkeeper would just open the gate every now and then to let fish through, but this lead to large numbers being picked off by predators as they waited. Then four years ago, the city came up with an ingenious solution - an underwater video livestream with a digital doorbell that people from anywhere in the world can press, when they see fish waiting to get on with their journey.

With the Netherlands' fish migration season already in full swing, here's how you can take part:

How do you use the fish doorbell?

It's easy and fun to get involved, and you can even leave it running in the background while you're doing something else, like working or watching TV. All you need to do is open the livestream on your computer, phone, or tablet here. The video feed should pop up towards the bottom of the page and start rolling automatically (although sometimes it needs a few refreshes).

You can see a counter letting you know how many other people are watching beneath the video, but the important part is just to the right. You should see a pink panel with a white button on it. This is what you need to click when you see a waiting fish.

When you do, a photo with a timestamp will be taken and sent to the lockmaster. When they receive enough of these alerts, they will open the gate to let the fish through.

You can take part from anywhere in the world, at any time. It doesn't matter if it's night-time in the Netherlands either, as this is actually when many species prefer to travel.

What kinds of fish you might see

Common species include members of the bream and perch families, but less common critters - sometimes species only found in the region - often make their way down the canal too.

These can include the silvery Dutch bindweed, or 'winde' fish, as well as different kinds of snake mackerel ('snoek'), and even eels ('paling'). Looking through the photo highlights on the website, other volunteers have even spotted curious crabs, or herons and cormorants feeding from time to time.