ONRWs (such as wetlands) are provided the highest level of protection under the antidegradation policy. The regulation requires water quality to be maintained and protected in ONRWs.
The Environmental Protection Agency (EPA) interprets this provision to mean no new or increased discharges to ONRWs and no new or increased discharges to tributaries to ONRWs that would result in lower water quality in the ONRWs. The only exception is to allow some limited activities that cause temporary and short-term changes in the water quality of an ONRW. EPA views temporary as weeks and months, not years.