Specific inquiries regarding the jurisdiction of the Corps of Engineers can be answered only after a determination whether (1) the waters are navigable waters of the United States or
(2) If not navigable, whether the proposed type of activity may nevertheless so affect the navigable waters of the United States that the assertion of regulatory jurisdiction is deemed necessary.
33 CFR § 329.15
Findings and determinations should be made whenever a question arises regarding the navigability of a waterbody. Where no determination has been made, a report of findings will be prepared and forwarded to the division engineer, as described above. Inquiries may be answered by an interim reply which indicates that a final agency determination must be made by the division engineer. If a need develops for an energency determination, district engineers may act in reliance on a finding prepared as in section 329.14 of this part. The report of findings should then be forwarded to the division engineer on an expedited basis.