The central Dutch city of Utrecht has installed a “fish doorbell” on a river lock that lets viewers of an online livestream alert authorities to fish being held up as they make their springtime migration to shallow spawning grounds. The idea is simple: An underwater camera at Utrecht's Weerdsluis lock sends live footage to a website. When somebody watching the site sees a fish, they can click a button that sends a screenshot to organizers. When they see enough fish, they alert a water worker who opens the lock to let the fish swim through. Much of the time, the screen is just a murky green with occasional bubbles, but sometimes a fish swims past. As the water warms up, more fish show up. “We get a lot of fan mail from people who think it’s slow TV and find it relaxing," said Anna Nijs, an ecologist with the Utrecht municipality. "Besides, they appreciate that they can actually do something to help.”
