Nowadays, accidental spills of crude oil are one of the most
worrisome environmental problems. Usually, the crude oil spills
rapidly inhibited photosynthesis of microalgae (the main primary
producers of aquatic ecosystems) causing a severe damage to inland waters ad marine ecosystems. In order to add knowledge about microalgal response to crude oil spill, here we study a fascinating example of extreme contamination by crude oil spills continuously (at least since 1915) in Arroyo Minero, Nirihuan de Arriba, Río Negro, Argentina. This study is changing our pre-conceived ideas on the adaptation of microalgae to crude oil. Astonishingly, a high biomass of microalgae proliferates in contact with crude oil. In contrast with the paradox of the plankton (which predict that more than 30 microalgal species would coexist in the same water body) only four species were detected in the crude oil spill area. They are cosmopolitan mesophile species and not extremophile ones (as would be expected). The most abundant species was the Chlorophyta Scenedesmus obtusus. Other abundant species seems
to be a new Scenedesmus species. The other two species Symploca dubia Cyanobacteria and Chlamydomonas dinobryonis Chlorophyta are new records for flora of Argentina. These species were isolated maintained in clonal laboratory cultures and characterised. They are resistant to crude oil of Arroyo Minero and to analytical petroleum special standard. In contrast similar species isolated from areas without crude oil contamination were destroyed by petroleum.