arm of the Pacific Ocean, indenting western British Columbia, Canada; it is an extension of Dixon Entrance and Chatham Sound, north of Prince Rupert. Named in 1793 by the English navigator George Vancouver in honour of the ducal house of Portland, the inlet is 25 miles (40 km) long and up to 8 miles (13 km) wide. Portland Inlet contains Pearse, Wales, and Somerville islands, receives the 236-mile- (380-kilometre-) long Nass River, and is continued north-northeast by the 30-mile- (48-kilometre-) long Observatory Inlet and Portland Canal (a 70-mile 【112-kilometre】 channel that is one of the world's longer fjords). Since 1903 Pearse Canal, north of the islands, and Portland Canal have served as the boundary between British Columbia and Alaska (U.S.). Copper is mined along the inlet's eastern shores.