In order to support the creation of sustainable and healthy ecosystems, citizens should have knowledge of the necessary maintenance needed. For example, they should be aware of the challenges of maintaining proper urban surface waters, so that they can take on a responsible and proactive role. Ideally, citizens should acquire this knowledge from an early age. We describe the design, implementation, and evaluation of the serious game Hydro Hero, aimed at forming and reinforcing this awareness and reasoning. Hydro Hero is an infinite runner game with extended minigames, which show both what should not be on the canals as well as why they should be removed. We assessed the ability of Hydro Hero to teach young children about canal maintenance by combining a questionnaire with open-ended play-testing sessions at a science museum. On average, players were able to improve their ability to justify why certain items should be removed or left in a canal. It has not been fully confirmed that Hydro Hero conveyed this specific knowledge, due to the absence of quizzing beforehand. However, given the high participants’ engagement, we consider the game to have contributed to their awareness about the importance of canal cleaning for a sustainable urban environment.