Laguna Teno (2549 m a.s.l.) is a high elevation oligo-mesotrophic lake located in the area of influence of the active Volcanic Complex Planchón-Peteroa (VCPP) in the central Chilean Andes. The most recent eruption of VCPP was in September 2010. This study compares limnological data registered in Laguna Teno during the summers of 2009 and 2011, pre- and post-eruptive periods of the VCPP activity respectively. In particular remarkable post-eruption changes of conductivity and slight changes for pH values in the water column of Laguna Teno were detected. In contrast no major variations of trophic parameters of water quality and plankton attributes were observed between the two summer periods. Phytoplankton was mainly represented by the biomass and chlorophylls attributable to diatoms, dinophytes and chlorophytes, with distinctive patterns of vertical segregation. Zooplankton was constituted by a very simple community comprising the copepod Boeckella gibbosa, the cladoceran Daphnia gr. pulex and a population of rotifers of the Hexarthra genus. This study represents the first limnological characterization of Laguna Teno and the first biogeographical report of a melanized population of the Daphnia pulex complex living in a deep high altitude Chilean lake. The limnological attributes of Laguna Teno, particularly the noticeable presence of large sized pigmented Daphnia in summer allow us to: i) infer the biological responses of Daphnia to extreme conditions; ii) support the hypothesis that Teno is currently a fishless lake. The latter presumption is consistent with the lethal effects on fish registered on the watershed of Teno and Claro rivers after the eruption of VCPP in 1991.