The organic micro-pollutants recently studied in the lake Leman waters and ecosystem are non-polar volatil substances and organochlorines like PCBs and DDT. The main volatil substances found are tetra- and trichloroethylene and 1,4 - dichlorobenzene. Concentration of this substances seems not ta be alarming. Pollution by DDT and its derivatives is decreasing, but the PCBs concentrations of coastal sediments and fishes can ta be considered as high and risk to produce a long-term contamination of the lake ecosystem. Eco-toxicological problems like a diminution of reproductive potential of the chars ("Salvelinus alpinus") would be related with the presence of organochlorine residues.