Captain Planet and the Planeteers (1990)

S2E10 An Inside Job

Sludge and four of the Planeteers experience the dire consequences of untreated sewage when MAL and Dr. Blight reduce the EcoSub—and themselves—to a microscopic scale, dropping them into contaminated water that Kwame accidentally consumes. To help Kwame recover, the Planeteers must confront grotesque waterborne parasites inside his body, all while figuring out how to return to their original size.