In the Spring, you can help man the fish doorbell. It's good fun for the second monitor, if you have one.

Context copied from the linked page:

"Every spring, thousands of fish swim through Utrecht’s canals and waterways, searching for a place to spawn and reproduce.

In the heart of the city lies the beautiful Weerdsluis, a manually operated lock. When the lock gates are closed, fish are forced to wait, wasting valuable time and energy – making them easy prey for birds and predatory fish.

To help the fish, an underwater camera is installed at the lock. If fish appear on screen, you can press the doorbell! This alerts the lock keeper, who will open the lock when many fish are waiting. You can “ring” the Fish Doorbell from early March to late May

People do so enthusiastically every year. In 2024, the Fish Doorbell attracted around 2.7 million viewers, from America to Brazil! The project has gained global recognition, helping people worldwide learn about fish migration and Utrecht’s underwater world."