This dataset was produced during a study investigating the impact of a small sewage source on the aquatic environment of the Caramagna Creek (NW Italy). At the study site, the creek receives an effluent sewer from a small cluster of houses. Macroinvertebrate community composition and abundance have been estimated monthly from January 2005 to March 2006 in two stations, located respectively 50 m upstream and 50 m downstream of the sewer pipe. At the same time, main physicochemical parameters, microbiological data, and chlorophyll-a concentration were assessed.