Ethnoichthyology, based on ecological parameters, can be a very useful tool to study man-made environmental changes. These changes are perceived by individuals who fish for a living and/or recreational activities in the impacted environs. The objective of this study was to investigate how the artisanal fisherfolk of the municipality of Carmo do Rio Claro, Minas Gerais, perceive the environmental changes caused by anthropogenic actions. The data were collected from August 2009 to January 2010 by means of openended interviews according to usual ethnographical techniques. Fifty professional fisherfolk were interviewed, forty-nine men and one woman. The results showed that they had experienced a reduction of fishing resources, the disappearance and/or rarity of some species, and the introduction of species. This pointed to the necessity of seeking the best ways to recover and conserve the native species of the Furnas Reservoir, in addition to a better monitoring of the introduced species.