Every spring, many fish species migrate from the Vecht, a branch of the Rhine River, to the shallow waters of the Kromme Rijn River to spawn and reproduce. However, their journey often stops at the Weerdsluis lock in Utrecht, Netherlands. The manually operated lock, designed to maintain the canal's water levels, rarely opens in the spring months. But now, thanks to an interactive "fish doorbell," the marine animals are able to reach their destination with little or no disruption.