Every year, freshwater fish species, including bream, bass, and pike, make a hazardous journey through Dutch waterways to reach their spawning grounds. Near Utrecht, a large city just 45 minutes from Amsterdam, migratory fish travel from the River Vecht to the shallower waters of the Kromme, an ideal location to spawn. Their route takes them through the city center, where they encounter many man-made obstacles, including the Weerdsluis boat lock.
Unfortunately for the fish, very little boat traffic passes through the lock in early spring, so the lock gates would normally remain closed, blocking their path. In 2021, local ecologists observed the buildup of fish below the closed lock. They realized that this made the fish more vulnerable to attacks from predators such as cormorants and other birds, so they devised an ingenious, crowdsourced solution.
A “fish doorbell” has now been installed in the waters below the lock. It’s a webcam that live-streams these murky green waters to a website, which members of the public can watch in real time. If they see a fish, a button on the webpage (essentially, the “doorbell”) allows viewers to alert the lock keeper, who will open the gates and allow the fish to travel upstream.
The webcam, now in its fifth year of seasonal operation from March to May, has proven immensely popular with viewers from around the world; the site had over 2.7 million viewers in 2024, and the doorbell button was pressed over 40,000 times. With many more viewers than fish, some of the website’s most avid supporters have clocked up hours of viewing but are still waiting for their big moment to spot a fish and ring the bell.
A fishy business:
- Aside from its practical function, the fish doorbell also supports ecologists’ efforts to better understand which species frequent the waters around Utrecht. Crabs, lobsters, and eels have been spotted in the webcam, in addition to a dozen fish species.
- In other areas, passive solutions such as fish ladders (a series of water steps that fish can jump up) have been deployed to mitigate the effects of manmade obstacles blocking migration routes. Currently a unique solution, the scientists behind the fish doorbell point out that it was much cheaper to install than a permanent fish ladder.
- Maintaining healthy fish populations is vital to the health of aquatic ecosystems, and the fish doorbell certainly isn’t the only remarkable effort to support annual migrations. In Washington state, an ingenious fish tube known as the “Salmon Cannon” uses a series of pneumatic tubes to gently move fish over dams located on several important migratory routes.
