Although explosive volcanic eruptions are natural disturbances that cause significant environmental repercussions and impose multiple changes on ecosystems, post-eruption studies of rivers and streams are not common. The most recent eruption of the Puyehue-Cord on Caulle volcanic complex (PCCVC) began on 4 June 2011 with a large explosion and the emission of a column of gas and volcanic ash (particle size <0.001-2 mm) followed by the release of silica magma, and lasted approximately until June 2012. The wind-dispersed volcanic ash affected the area surrounding the PCCVC in southern Chile and, subsequently, most of South America, but local effects on streams and rivers in the vicinity were more drastic. We collected water, ash, and benthic macroinvertebrate samples four months after the eruption from four rivers: Two were visibly impacted (Gol-Gol and Nilahue) in areas where volcanic ash thickness ranged between 1 and 5 cm, in the vicinity of the PCCVC fissure (8-15 km), and two adjacent rivers (Calcurrupe and Chanleufu) were located 20-40 km from the PCCVC fissure where ash thickness was <1 cm and did not present visible impacts. Results were then compared with data obtained from previous research projects. This study reports that this natural disaster induced an increase in concentrations of total suspended solids and of phosphorous in the rivers Gol-Gol and Nilahue, as well as habitat destruction, deterioration of environmental quality, and the consequent devastation of macroinvertebrate assemblages inhabiting these rivers directly following the eruption. We conclude that volcanic eruptions can generate local extinctions of benthic macroinvertebrates in the short term, compared with rivers that were not affected by volcanic ash.