Background.

Many streams of Uruguay suffer eutrophication and physical pollution due to intensive farming. The Colorado stream, in the coastal plain of the Rio de la Plata, is a particular case, which also receives winery debris. Macroinvertebrates give comprehensive information status of aquatic systems.

Goals.

To assess the overall environmental quality of the river Colorado, both water quality and the habitat and macroinvertebrate fauna was studied.

Methods.

Six sites were sampled: two on the Colorado stream and two on each headwater: Benitez and Rocha creeks.

Results.

Benitez creek receives effluents from wineries and presented high conductivity and low oxygen concentration. Rocha creek instead shows higher levels of nutrients and lower conductivity. We identified 787 invertebrates belonging to 3 orders of crustaceans and 6 of insects, 2 families of Diptera, 7 of molluscs and 2 of annelids. In Rocha creek taxonomic richness was below average. The study sites downstream in Rocha creek and Colorado river had richer and more equilibrated communities indicating a possible recovery.

Conclusions.

In all sites tolerant species to organic pollution dominated. Rocha creek suffers eutrophication, but still has some self-purification capacity downstream, while Benitez creek deteriorates perhaps from impact of wineries, which remains until it meets the Rocha creek, interrupting the recovery process.