Maps

Existing Use establishes protection for a waterbody on or after November 28, 1975 whether or not that use is included in the water quality standards (25 Pa. Code §93.1 and 40 CFR §131.3(e)). Existing Use is different from a Designated Use; Designated Use is defined for each waterbody or segment whether or not the use is being attained. Existing Use is the actual use the waterbody is attaining at the time of an evaluation. The Department maintains a publicly accessible list of surface water segments where data has been evaluated which indicates an existing use classification of a waterbody that is more protective than the designated use (including those segments which are HQ or EV). Only an existing use which is more stringent than the designated use in §§ 93.9a - 93.9z for a particular waterbody is placed on the existing use list. This GIS watershed layer (which is not part of the Water Quality Standards) is offered to provide a spatial representation of the Aquatic Life Use Tiers contained in the portion of the Pennsylvania Code referenced above. These spatial representations are intended to supplement the Water Quality Standards but should not be substituted for the official version of the standards found in the Pennsylvania Code.

Water quality criteria are used to protect designated water uses, such as fish and aquatic life, recreation, and water supply. Designated uses establish the reason for protection and the water quality criteria define the criteria required to protect that benchmark. Use designations and water quality criteria together, constitute Pennsylvania Water Quality Standards as defined in Title 25 Environmental Protection, Department of Environmental Protection, Chapter 93. This GIS watershed layer (which is not part of the Water Quality Standards) is offered to provide a spatial representation of the Aquatic Life Use Tiers contained in the portion of the Pennsylvania Code referenced above. These spatial representations are intended to supplement the Water Quality Standards but should not be substituted for the official version of the standards found in the Pennsylvania Code.

Sufficient dissolved oxygen (DO) is crucial for the fauna of the Chesapeake Bay to exist. Different aquatic organisms have different DO requirements. Many finfish need at least 5 mg/l while some bottom dwelling worms and clams need as little as 1 or 2 mg/l to survive. The different designated use zones (Open Water, Deep Water and Deep Channel) reflect the different needs of the species that inhabit different parts of the water column. Note: Some areas of the DO Designated Use were changed in 2007 from the original published map of 2003.