The number and extent of so-called marine “dead zones” -areas of coastal ocean waters where nearly all forms of marine life have been snuffed out due to lack of oxygen—has been on the rise for decades now, posing increasing threats to commercial and subsistence fisheries, recreational fishing and human health. Terrestrial runoff containing relatively high levels of phosphorous, primarily from agricultural fertilizers, has been identified as one of the main culprits. Wastewater discharge from cities and urban centers is also to blame.