P.E.I. has a very gradual shoreline in many places, so shallow waters will naturally warm up much faster during the day and some beaches can feel like bath water within sandbars. Beaches on the Northumberland Strait do have warmer waters than Northern beaches.

Prince Edward Island (PEI) is famous for having the warmest ocean waters north of the Carolinas, often reaching 20°C (68°F) or higher in August. This phenomenon is caused by the shallow nature of the Northumberland Strait, which separates PEI from the mainland. Because the water is shallow and protected from the cold, deep-ocean currents of the Atlantic, it heats up rapidly under the summer sun—much like a giant tide pool. Furthermore, the island's unique "cupped" geography and the lack of significant cold-water upwelling allow the surface temperatures to remain high throughout July and August. While the North Shore beaches are slightly cooler due to being open to the Gulf of St. Lawrence, the South Shore beaches benefit from the gentle, sun-warmed currents of the Strait, making it the premier destination in Canada for swimming and beach-going during the late summer months.