Kāneʻohe Bay, at 45 km², is the largest sheltered body of water in the main Hawaiian Islands. This reef-dominated embayment constitutes a significant scenic and recreational feature along the northeast coast of the Island of Oʻahu. The largest population center on Kāneʻohe Bay is the town of Kāneʻohe.
The Bay is approximately 8 mi long and 2.7 mi wide, with a mouth opening of about 4.6 mi wide and a maximum depth of 40 ft in the dredged channel. It has one of the two barrier reefs in the archipelago, the other being the 27 mi barrier reef of Molokaʻi island, and also has extensive development of shoaling coral reefs within a large lagoon. Two navigable channels cut across the northern and southern ends of the barrier reef. The deeper, northern channel, located off Kualoa Regional Park, provides entrance from the North Pacific Ocean to a ship channel dredged the length of the lagoon between 1939 and 1945. The lagoon contains extensive patch and fringing reefs and its southern end is partly enclosed by the Mokapu Peninsula. This peninsula is occupied by Marine Corps Base Hawaii.
There are five named islands or islets within Kāneʻohe Bay.