A salt marsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open salt water or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. Salt marshes have been disintegrating and dying over the past two decades along the U.S. Eastern seaboard and other highly developed coastlines, without anyone fully understanding why. This week in the journal Nature, MBL Ecosystems Center scientist Linda Deegan and colleagues report that nutrients—such as nitrogen and phosphorus from septic and sewer systems and lawn fertilizers—can cause salt-marsh loss.