Nahuel Huapi is a glacial lake located along the eastern slope of Southern Andean Range with a maximum length of 67 km and a maximum width of 10 km. The lake resembles in its shape "a gigantic amoeba with enormous tentacles extending in all directions to form (1)" a number of arms or fjords. It is also encircled by many smaller lakes. Mountains fringe almost all its coastline; there is a succession of bays and coves, shingle and sandy beaches, perpendicular rocky cliffs, steep promontories, and wooded isthmuses and peninsulas.

The lake offers one of the nicest landscapes in South America, and has been included since 1909 in Nahuel Huapi National Park, the largest of Argentine national parks (785,000 ha). The international city of San Carlos de Bariloche, growing up very fast on the southeastern margin of the lake, attracts every year lots of tourists with pleasant summer weather and winter sports.

The report of a Swedish South-American expedition in 1953-1954 (1) states that "the luxuriant forests of Austrocedrus and Nothofagus surrounding its solitary fjords contrast with the scanty aquatic macrophytes" and that "the scarcity of the latter is partly dependent on the very limited shallow water areas..." This situation, however, changed in the last years when a rapid cultural eutrophication was observed in some small and less deep inlets of the lake, particularly near the city of Bariloche, though the main body of Nahuel Huapi remains oligotrophic. Thus, a lot of macrophytes, especially Scirpus californicus, cover those inlets and are expanding in some arms. Those arms are also rich in nutrients and phytoplankton owing to the result of human activities. Protective measures should be taken before the eutrophication and other kinds of pollution spoil the value of the National Park, where the municipal authorities of Bariloche have jurisdiction of administration (Q).