A blue whale, the largest animal ever to have lived on earth, can be as long as three city buses, weigh more than 20 elephants and shoot up a spout of water as high as a three-story building with its exhalation.

"You need to see one," recommended Susan Sherman of the Oceanic Society.

Now may be your chance.

This summer, lots of the behemoths are just off the Northern California coast, in larger numbers and earlier in the season than usual.

Since the beginning of June, from Monterey Bay and up to the coast off San Francisco, lucky whale-watchers have caught glimpses of the elusive mammal.

"We started having blue whales on every trip we went out on," said Sherman, who runs weekend whale-watching and natural history excursions from San Francisco to the Gulf of the Farallones with the Oceanic Society. "It hasn't been this great for the past five years."

Her explanation: "They're in this area because the food is here."

"We don't always have such dense krill," said Nancy Black. The small crustaceans almost exclusively make up a blue whale's diet. In a day, a blue whale eats about four tons of krill, said Black, who runs Monterey Bay Whale Watch.

They are here to get it.

There are "perfect conditions this year," said Black. She predicted between eight and 40 blue whale sightings in one of her roughly four-hour tours of Monterey Bay.

"There should be more blue whales that we might catch on our way back as well," she said to her passengers as she was interviewed by phone.

An endangered species, 10,000 blue whales are estimated to live worldwide. Around 2,000 are regularly off the Pacific Coast, from Central America to Alaska.

"Blue whales tend to move around," said John Calambokidis of Cascadia Research, a marine mammal research organization. "These sorts of variations in concentrations of whales is a pretty common occurrence up and down the coast," he said.

This winter, storms brought nutrients from the ocean's bottom to the surface off Northern California. This spawned growth of more phytoplankton, the "microscopic plants of the ocean," said Donald Croll, UC Santa Cruz marine biologist.

Rippling up the food chain, more phytoplankton supports the lives of more small marine animals, such as krill, which attract the larger ones that eat them.

Blue whales aren't the only ones lured by the abundant food supply.

"The birds are spectacular; there are hundreds of thousands," Sherman said.

Humpback whales, dolphins, basking sharks, orcas and other species are likely to be seen in Monterey Bay and up the Pacific to Bodega Bay, said Black and Sherman.

"This has been a good year, a very, very good year for the animals," Sherman said.

"It's something you can't see on Animal Planet, that's for sure," said Ken Stagnaro, one of the captains of Santa Cruz Whale Watching, of the variety of animals.

It's hard to say for how much longer the whales and other wildlife will stick around. "It probably won't end overnight," Black said in early July. "But hopefully a few more weeks. It's unpredictable; we just don't know."

Sherman agreed. "We don't know how the summer's going to go," she said. She notes cautiously that there is "no guarantee that you'll see a blue whale when you come out."

"You don't have to go to some place like Africa to see these wild animals," Black said. "They're in our own backyard."

"It's a privilege to be able to have this, and right on our doorsteps," Sherman said.

For perspective, Sherman offered another image of the massiveness of a blue whale: Given the opportunity, a small child could swim through its aorta, the heart's major blood vessel.

"Everyone I know that has seen one is like, 'Oh my gosh, this is so big,' " she said.

"It humbles you."

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