As announced in the Federal Register Vol. 82, No. 42 (https://www.gpo.gov/fdsys/pkg/FR-2017-03-06/pdf/2017-04312.pdf):
Through new rulemaking, the EPA and the Army seek to provide greater clarity and regulatory certainty concerning the definition of “waters of the United States,” consistent with the principles outlined in the [recent] Executive Order and the agencies’ legal authority.
Agencies have inherent authority to reconsider past decisions and to revise, replace or repeal a decision to the extent permitted by law and supported by a reasoned explanation. Importantly, such a revised decision need not be based upon a change of facts or circumstances. A revised rulemaking based “on a reevaluation of which policy would be better in light of the facts” is “well within an agency’s discretion,” and “[a] change in administration brought about by the people casting their votes is a perfectly reasonable basis for an executive agency’s reappraisal of the costs and benefits of its programs and regulations.”