Fishtronaut and Rosybarb notice a rainbow-colored oil slick on the lake surface, that spreads fast! They know it can make the water very polluted. The POP offers a few clues and with help from Marina and Zeek, Fishtronaut starts to investigate where the oil is coming from. During their journey, they learn about ways to clean up the dirt caused by oil leak, and how to prevent it from happening.