FILIPPOVA et al. absence of oxygen at a depth of 80–90 m, the concen tration of dissolved methane reaches 21 mM . The high pH of this mixed water mass (pH 10.2–6.9) has been attributed to weathering of the predominant anorthosite rock in the lake s hollow [11, 12]. The benthic environment is dominated by cyanobacterial mats forming cuspate pinnacles dominated by Lep tolyngbya spp. and laminated, conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp..