Ocean Dead Zones
80% of US agricultural land is used for raising animals and feed crops. The agricultural runoff from this land creates hypoxic dead zones in the rivers and the ocean in which all fish die off. The most notorious is the Jersey-sized dead zone at the mouth of the Mississippi in the Gulf of Mexico.
The breakdown of land use in the United States is provided by the US Department of Agriculture (USDA), but of late, these USDA reports appear to have become obscured and difficult to obtain. However, there is a repository of full USDA reports in University web sites and the above statistic comes from a report published by Vesterby and Krupa of the USDA here. The linkage between agricultural runoffs and ocean dead zones is well known as discussed here.