This report assesses the state of the science on the environmental impacts of mountaintop mines and valley fills (MTM-VF) on streams in the Central Appalachian Coalfields. These coalfields cover about 48,000 square kilometers (12 million acres) in West Virginia, Kentucky, Virginia, and Tennessee, USA. Our review focused on the impacts of mountaintop removal coal mining, which, as its name suggests, involves removing allor some portionof the top of a mountain or ridge to expose and mine one or more coal seams. The excess overburden is disposed of in constructed fills in small valleys or hollows adjacent to the mining site. Our conclusions, based on evidence from the peer-reviewed literature, and from the U.S. Environmental Protection Agencys Programmatic Environmental Impact Statement released in 2005, are that MTM-VF lead directly to five principal alterations of stream ecosystems: (1) springs, and ephemeral, intermittent, and small perennial streams are permanently lost with the removal of the mountain and from burial under fill, (2) concentrations of major chemical ions are persistently elevated downstream, (3) degraded water quality reaches levels that are acutely lethal to standard laboratory test organisms, (4) selenium concentrations are elevated, reaching concentrations that have caused toxic effects in fish and birds and (5) macroinvertebrate and fish communities are consistently degraded.