This study was carried out between December 2015 and August2017, in order to assess the physico-chemical quality and lead contamination of Lake Tonga's surface sediments, a Ramsar site of international importance. Many physico-chemical parameters were considered in this work, among them: pH, redox potential, conductivity, organic matter, cation exchange capacity, chloride, sulfate.... Sediment sampling was carried out from 8 stations. The physico-chemical characterisation of sediments revealed a pH close to neutral to alkaline. Spatio-temporal variations in electrical conductivity show significant fluctuations over the differentstations and over seasons. Organic matter levels recorded during the rainy period were much higher than those of dry period. The highest concentrations of Cation Exchange Capacity were observed during the cold period and the highest concentrations of chloride ions were recorded during the wet season. The winter period was the most heavily loaded with SO4- ions. Analysis of lake sedimentsreveals an increase of lead levels in the direction of the dry season and wet season. Mean lead concentrations were all above the TEC guide inducingoccasionally effects on benthic fauna. The resultsobtained confirm an enrichment or even contamination by this element. Rigorous monitoring should be conducted to protect this siteand its biodiversity