Mercury is a trace metal known for its neurotoxicity, especially its organic species, collectively known as methylmercury (MeHg). MeHg is not usually released in the environment but produced by biotic processes driven by several groups of obligate anaerobes present in the anoxic bottom sediments of aquatic ecosystems. However, in recent years, many researchers have shown that this methylation also occurs along the oxic water column in relation to a high content of particulate organic matter known as marine and lake snow. The present thesis aimed to investigate the lake snow as a micro-niche for MeHg production along the water column of a deep peri-alpine lake (Lake Geneva-Switzerland/France). MeHg concentrations found in Lake Geneva lake snow showed higher values than in bottom sediments, with increasing concentrations with depth along the water column. Furthermore, the concentrations of particulate matter showed a decrease with depth, probably due to predation by zooplankton and fish. Moreover, hypoxic and anoxic microenvironments were found in the settling aggregates highlighting the possibility for lake snow to act as an anoxic substratum for Hg methylators. The findings presented in this thesis show that lake snow, as marine snow, has the ability to be an important micro-niche for MeHg production in oxic environments.