Nantucket Sound is a large, open saltwater sound located between Cape Cod, Martha's Vineyard, and Nantucket. It functions as a massive tidal basin, filling and draining through three main channels: Vineyard Sound, Muskeget Channel, and Great Round Shoal Channel. Tidal currents in these conduits and around points and headlands are significant, flowing at 2 to 3 knots or higher. For paddlers, timing passages to coincide with favorable currents is critical, as fighting a foul current can drastically reduce progress. The tidal range also affects the many rivers and marshes that feed into the sound, with low tide exposing vast mud flats in areas like the Herring River and Nantucket Sound's own shoreline, which can strand paddlers.

Access to the sound is primarily through the numerous harbors, rivers, and inlets along the Cape Cod coastline. Specific launch points include the shoreline at Dennisport, the mouth of the Swan River in Dennis Port, and Long Beach in Centerville facing the sound. The Swan River offers a protected paddle through marshes before opening into the sound, with a public town beach on its west bank near the mouth. Paddling directly on Nantucket Sound is an open-water adventure suited for experienced kayakers due to exposure. Wind can quickly create choppy conditions, and once on the sound, paddlers may encounter waves of two feet or more. Boat traffic is a consideration, and it is advised to launch early in the day before recreational traffic increases.

The sound's shoreline features a mix of developed areas with waterfront homes and natural conservation lands. Wildlife sightings can include harbor seals, various waterfowl like herons and egrets, and ospreys. The area around Monomoy Island, at the sound's eastern edge, is known for seal colonies but is recommended only for advanced paddlers due to strong currents, shifting weather, and complex tides. Several kayak outfitters and tour guides operate along the Cape Cod coast, providing instruction, rentals, and guided trips for those less familiar with the sound's dynamic conditions.