Virginia's antidegradation policy protects water quality at three levels or "tiers".
- Tier 1 specifies that existing instream water uses and the level of water quality to protect the existing uses shall be maintained and protected. This means that as a minimum, all waters should meet adopted water quality standards.
- Tier 2 protects water that is better than specified water quality standards. Only in limited circumstances may water quality be lowered in these waters.
- Tier 3 are exceptional waters where no new, additional or increased discharge of sewage , industrial wastes or other pollution are allowed. These waters must be specifically listed in the regulation.