The term "Inside Passage" is also often used to refer to the ocean and islands around the passage itself. The Inside Passage is also sometimes referred to as the "Inland Passage" which is in turn a reference to early explorers' quests to locate the Northwest Passage between the Pacific Ocean and the Atlantic Ocean.
The Alaskan portion of the Inside Passage extends 500 miles (800 km) from north to south and 100 miles (160 km) from east to west. The area encompasses 1,000 islands, 15,000 miles (24,000 km) of shoreline and thousands of coves and bays. While the Alexander Archipelago in Alaska provides some protection from the Pacific Ocean weather, much of the area experiences strong semi-diurnaltides which can create extreme 30-foot (9 m) differences between high and low tide, so careful piloting is necessary in many places in order to not collide with underwater obstructions.