This document, summaries the three IUCN/UNEP submissions to the World Commission on Dams. The current report focus on summarising the specific aspect of environmental and ecosystem impacts of large dams. It is not intended to provide the wider scope or analysis of large dam issues. The document does not present a specific framework of action, but rather provides a benchmark of current status. It provides an overview of present understanding of the impact of dams on ecosystems and biodiversity. It describes measures for ameliorating the negative environmental impacts and outlines mechanisms that historically have promoted approaches to avoid, mitigate and compensate negative environmental impacts. Mechanisms for funding amelioration interventions and ensuring developer compliance with such measures are presented.