Concerning the impact of organic contamination, most studies focus on the main river courses, which are affected by large wastewater plants and intensively urbanized areas, while a large part of a river's catchment area is made up of small streams flowing through rural or forested areas. As a result, the impact of even small sources of organic load on small systems is often not analysed. This study investigated 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. To evaluate the impact of this point source of pollution, we estimated macroinvertebrate community composition and abundance 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. These data aim to inspire additional research, particularly in addressing the implications of often overlooked small impacts occurring in small rivers, which can have an enormous impact given the dendritic organisation of the hydrographic network and the multiplicative effect along the river system. These results are especially relevant in the context of evolving river dynamics influenced by decreasing flows, resulting in a diminution in dilution capacity and thus greater fragility of river ecosystems. Moreover, if we consider only the upstream site, this dataset holds important potential related to non-impacted macroinvertebrate communities, constituting an important reference because it integrates macroinvertebrate community data with different environmental data, from granulometry to in-stream productivity, from chemical-physical to microbiological data.