New sustainability and environmental criteria are currently being developed for the provision of green bonds and other forms of climate finance. These criteria are increasingly requiring more detailed assessments of greenhouse gas (GHG) emissions, including those caused by the creation of a reservoir. The G-res Tool is a publicly available web-based tool which allows hydropower companies, investors, consultants, decision-makers and other stakeholders to more accurately report on the net impact of GHG emissions resulting from the introduction of a reservoir to a landscape. The tool works for both existing and planned reservoirs and allows for the allocation of emissions to the various water-uses of a reservoir and to the other anthropogenic activities in the catchment. This presentation will provide attendees with a background on the science of GHG emissions from reservoirs, an overview of international standards for carbon emissions from hydropower reservoirs. It will also introduce the G-res Tool interface and how it works and will conclude with a brief overview of worldwide GHG emissions trends.