The Araucania region (38° S, Chile) originally had native perennial forest in middle valleys regions, that was gradually replaced by towns and agricultural zones during the last century, nevertheless there is some relicts of these native forests that are preserved, one of these relicts is Rucamanque, a protected area in the surrounding of Temuco town. The aim of the present study was a first aquatic Arthropoda description in a stream of this protected area using species co-occurrence and niche overlap null models. The results of species co-occurrence null model revealed that species associations are random, whereas the results of niche sharing revealed that species reported have different ecological niches, and in consequence there is not interspecifi c competence. The exposed results revealed the presence of aquatic fauna representative for unpolluted streams; similar descriptions were found for other similar inland water ecosystems in Argentinean and Chilean Patagonia.