A grey whale was spotted in False Creek, south of Vancouver's downtown peninsula, between the Granville Street and Burrard Street bridges, on Wednesday morning.
A Canadian Coast Guard vessel followed the unlikely visitor after it was first noticed in the busy harbour just before noon.
Australian tourist Rob Fletcher was one of the lucky few who caught sight of the whale. He spotted it while on board a passenger ferry.
"It was just a hump as it broke the surface," he said. "It was a grey hump, and it shot a small spurt of water in the air.
"It was fabulous. We travelled a long way to see a whale, and you normally pay a lot of money to go and see a whale on a whale cruise, and we saw one for $4. It was pretty spectacular."
The grey whale was eventually led back into open waters by the coast guard and the Department of Fisheries and Oceans.
Grey whales were nearly hunted to extinction on the West Coast of North America by the 1970s, but in recent years their numbers have been recovering and many have been spotted in areas where they've not been seen for decades.
False Creek is a saltwater inlet south of downtown Vancouver. It was once a heavily polluted industrial harbour but was cleaned up in recent decades and is now mostly used by recreational boaters.
Last week, a grey whale was spotted several kilometres north of Vancouver near Squamish, at the north end of Howe Sound. It is not known whether the two sightings were of the same whale.