Antidegradation refers to federal and state regulations designed to maintain existing uses of surface waters and to protect high quality waters from unnecessary pollution. An Outstanding Iowa Water (OIW) is defined as the following: "A surface water that IDNR has classified as an outstanding state resource water in the water quality standards." An OIW receives Tier 2 ½ protection. Tier 2 ½ Review is defined as follows: "Policies and procedures that prohibit any lowering of water quality in unique waters as identified in the water quality standards unless the lowering is temporary and limited, results from expansion of existing sources, or serves to maintain or enhance the value, quality, or use of the OIW, as determined by the Director of IDNR on a case-by-case basis."

Tags: water quality, outstanding water, streams