The Long Island beaches with the best water quality are on the North Fork at McCabes, Town Beach and Orient State Park in Southold. The Connecticut beaches with the best water quality are Hole In The Wall Beach in East Lyme, Esker Point Beach in Groton and Surf Club Beach in Madison.

The clearest water on Long Island is generally found on the East End, particularly in the bays and beaches around Shelter Island and the North Fork. Places like Menhadden Lane Beach on Shelter Island and Orient Beach State Park are famous for their crystal-clear visibility, often allowing you to see several feet down to the sandy bottom on a calm day. This clarity is due to the rocky or pebbly nature of the ground, which prevents sand from clouding the water, combined with excellent water circulation from the Long Island Sound and the Peconic Bay. On the South Shore, Coopers Beach in Southampton is frequently cited for its cleanliness and Caribbean-like turquoise hues, though the Atlantic surf can sometimes stir up the sand. For a truly pristine experience in 2026, locals recommend visiting the secluded sandbars of Nassau Point in Cutchogue or taking a boat to the private Robbins Island, where the lack of development and boat traffic keeps the water exceptionally transparent and inviting for swimming and snorkeling.