The “fish doorbell” is back to help Utrecht’s aquatic population navigate canals. Fish swim through the Dutch city every spring in search of a place to spawn and reproduce – but the Weerdsluis lock in the west of the city is rarely opened at this time of year. To help fish on their way, the city introduced a fish doorbell four years ago, manned by strangers on the internet. Volunteers can tune into a livestream of an underwater camera and when they see a fish, they can press a digital door bell which alerts the lock operator. The bell has been a big hit on social media. Viewers of the livestream sometimes pause to identify different species before ringing the bell. Want to put a finger on the button? Visit the fish doorbell website.