Uruguay has a dense hydrographic network, nevertheless the knowledge of the aquatic macroinvertebrate community is still lacking. In recent decades afforestation with exotic species has increased which has produced changes in riparian vegetation of some rivers. The aim of this research was to determine the composition and trophic structure of macroinvertebrate community and its relationship to some physicochemical parameters in eight streams where the native forest is still well preserved and provide the basis for future studies. Samples were collected from December 2006 to December 2007. Temperature, dissolved oxygen, pH and conductivity were measured in situ. Taxonomic composition and abundance were determined, a principal component analysis and a canonical correspondence analysis were carried out with the physico-chemical and biological parameters. The alpha diversity was calculated using the Shannon-Weaver (H'), dominance of Simpson (D) and Pielou evenness indexes (J'). Beta diversity was determined employing similarity index of Bray-Curtis. A total of 1 291 specimens belonging 92 taxa were recorded. The most abundant taxa were Ephemeroptera (36%), Amphipoda (17%) and Coleoptera (12%). The streams show high diversity and low dominance. Conductivity, pH, and temperature were the main factors in determining the macroinvertebrate distribution and composition.

The Chilean fauna of amphipods has been poorly studied. Freshwater amphipods in Chile have a single genus in epigean environments. Seven species of the genus Hyalella are reported for Chile: H. simplex; H. fossamancinii, H. kochi; H. chiloensis; H. costera; H. araucana, and H. franciscae. A short diagnosis, a key and figures are given for each species<br>La fauna de anfípodos chilenos ha sido pobremente estudiada. En el caso de los de agua dulce y de ambientes epigeos, el grupo está representado solo por un género. Se reportan siete especies del género Hyalella para Chile: H. simplex; H. fossamancinii, H. kochi; H. chiloensis; H. costera; H. araucana, y H. franciscae. Se entrega una breve diagnosis, una clave y figuras para cada especie