"An adequate level of dissolved oxygen is necessary to support most forms of aquatic life. While very low levels of dissolved oxygen (hypoxia) can be natural, especially in deep ocean basins and fjords, hypoxia in coastal waters is mostly the result of human activities that have modified landscapes or increased nutrients entering these waters. Hypoxic areas are more widespread during the summer, when algal blooms stimulated by spring runoff decompose to diminish oxygen. Such hypoxic areas may drive out or kill animal life, and usually dissipate by winter. In many places where hypoxia has occurred previously, it is now more severe and longer lasting; in others where hypoxia did not exist historically, it now does, and these areas are becoming more prevalent. […] As knowledge and understanding have increased concerning the possible impacts of hypoxia, congressional interest in monitoring and addressing the problem has grown. The issue of hypoxia is seen as a search for (1) increased scientific knowledge and understanding of the phenomenon, as well as (2) cost-effective actions that might diminish the size of hypoxic areas by changing practices that promote their growth and development. This report presents an overview of the causes of hypoxia, the U.S. areas of most concern, federal legislation, and relevant federal research programs. This report will be updated as circumstances warrant."
CRS Report for Congress, 98-869