The combined Ipswich River/Plum Island Sound exits through a relatively narrow, shallow channel that passes under Castle Hill and along Crane's Beach to the south. On the north, Sandy Point at the tip of Plum Island juts into the flow. In the days of sail, Bar Head, Bar Head Rocks, and Emerson Rocks posed some threat to sailing vessels trying to tack into or out of the estuary. The shallow waters often stranded vessels in storms, which would then be dismantled by severe breakers. The combination was inevitably tragic to vessels caught there in a northeaster, or violent winter storm of near-hurricane-force winds. Despite these difficulties, the sound and the mouth of the Ipswich were mooring places of ocean-going cargo vessels and fishing and whaling boats, before the opening of Newburyport Harbor, then blocked by a sandbar. The now abandoned shores of the region give little hint of its former importance to commerce and prosperity.