19 CFR § 4.6 - Departure or unlading before report or entry.
(a) No vessel which has arrived within the limits of any Customs port from a foreign port or place shall depart or attempt to depart, except from stress of weather or other necessity, without reporting and making entry as required in this part. These requirements shall not apply to vessels merely passing through waters within the limits of a Customs port in the ordinary course of a voyage.
(b) The “limits of any Customs port” as used herein are those described in § 101.3(b) of this chapter, including the marginal waters to the 3-mile limit on the seaboard and the waters to the boundary line on the northern and southern boundaries.
(c) Violation of this provision may result in the master being liable for certain civil penalties and the vessel to arrest and forfeiture, as provided under 19 U.S.C. 1436, in addition to other penalties applicable under other provisions of law.