A three-year-old grey whale managed to swim away at high tide Monday night, after sparking a desperate rescue effort when it became beached on tidal flats south of Vancouver.

However, it's still unclear whether the whale, which experts say is very sick, will survive.

Off-duty Delta firefighters ran a fire hose from a hydrant to spray cold water on the whale earlier in the day, biding time until the tide came in.

Volunteers and members of the Vancouver Aquarium attempt to save a beached Grey Whale near Vancouver, Monday. (CP Photo)

The whale was stranded on sand in Boundary Bay near the town of Tsawwassen, about 30 kilometres south of Vancouver.

The bay is so shallow that the whale was a whole kilometre from the water's edge at low tide.

Officials with the Vancouver Aquarium put a canopy over it to ward off the sun's rays and covered its tail with towels to keep it cool and wet.

A spokesman for the aquarium wasn't optimistic about the animal's chances of survival earlier in the day, noting that it appeared starving and dehydrated.

Dr. David Huff said the whale probably beached itself because it no longer had enough strength to swim.

"She hasn't eaten in a long time," he said. "They get their water from their food, so she would absolutely become dehydrated. And the other really big factor is exposure, which we're solving for now with the water and everything."

Huff also said the whale's weight puts a big burden on its internal organs, especially the lungs – limiting its ability to breathe.

The Department of Fisheries and Oceans sent vessels to the beach to try to tow the whale if it hadn't managed to swim away on its own.

If that had failed, officials said the whale might have had to be euthanized.

It's believed the young whale was migrating north from Mexico's Baja Peninsula to the Bering Sea.