Before EPA approved a decision by the Louisiana Department of Environmental Quality to reduce the required dissolved oxygen level of the stream segments to 2.3 milligrams per liter from March through November, all of the affected waters were supposed to have oxygen levels no lower than 5 milligrams per liter for freshwater segments and no lower than 4 milligrams per liter for estuarine rivers and streams year-round in areas where freshwater and saltwater systems mix. The change would effectively allow businesses and others in the rivers' watersheds to increase their release of pollutants into the water, such as fertilizer and other nutrients, the environmental groups argue, which could result in algae blooms or other changes in water quality.