[en] A first document proposes an overview of the different aspects of the ecological monitoring studies performed during 20 years to assess the environmental footprint of the Petit Saut dam in French Guyana. After an introduction recalling the history of these scientific works, and highlighting how this site is a reference for hydraulics studies in tropical environment, the contributions address aquatic biodiversity (water chemistry, creation of an aerator weir, aquatic invertebrates, fishes), the mercury issue (understanding of mechanisms of contamination by mercury, presence of mercury in fishes), the greenhouse gases (evolution of emissions from the lake and from the downstream water, site of major scientific contribution), the rescue and safeguarding of land wildlife (the wildlife operation, the safeguarding operation). A set of Power Point presentations proposes numerous data and results. The first one illustrates the role of the Petit Saut scientific committee: context and first actions (creation of the scientific committee, the Petit Saut Laboratory for the environment), and the scientific programmes (on land wildlife, on aquatic biodiversity and water quality, on mercury in Guyana, on hydroelectric production and greenhouse gases). A Power Point presentation of 20 years of studies and monitoring of the hydro-biology of the lake is then proposed: general presentation, physics and chemistry, fishes, benthic, pelagic and land invertebrates. The next Power Point presentation concerns greenhouse gas emissions: climate and greenhouse gases, hydroelectricity and greenhouse gases, case of Petit Saut. The next ones concern the mercury issue (sources of contamination, mercury chemistry, bio-accumulation and bio-amplification mechanisms, distribution of fish contamination, effects on human health), and the rescue and safeguarding of land wild life (programmes and main results, data valorisation, prospective and perspectives).