A grey whale has made a surprise visit to Howe Sound, making a detour to feed well off the course of its usual migration path.

The massive whale can be seen swimming at the mouth of the Squamish River in a video posted on YouTube.

Whales of its species often pass through the coastal waters of B.C. during their seasonal migration from California to Alaska, but generally pass by on the western side of Vancouver Island.

"It's a chance to see a species which, for some people in some parts of the world, is very common, and for people in the Vancouver area is less common," Andrew Trites, a marine mammal scientist at the University of B.C., told ctvbc.ca.

Greys are often seen in Boundary Bay in the springtime, however, when they feed on crustaceans in the shallow mudflats.

The mammal appears energetic in the video, meaning it is probably having no trouble feeding itself.

"From what I've heard of this whale, it seems to be healthy and feeding. It's probably only in for a quick snack and then heading up north again," Trites said.

"We're at a time of year when grey whales are moving north from the lagoons in Mexico, and every springtime, there's always a few whales that seem to wander off track."