SANTA CRUZ, Calif. -- Grab your camera and binoculars: There's rarely been a better time to go whale-watching off the California coast.

Tourists from around the world have been flocking to Monterey Bay to catch a glimpse of the massive marine mammals, including impressive numbers of blue whales, the largest animals on earth.

Longtime observers say they've seen a sharp increase in endangered blue and humpback whales feeding near California shores, where they spend the spring and summer before heading to their winter breeding grounds off Mexico and Central America.

"It's phenomenal that these humongous creatures are out there and we just get to go out on a boat and go out and watch them," said Santa Cruz resident Susan Stuart after a recent whale-watching cruise.

What's bringing the whales so close to shore? A bumper harvest of their favorite food: tiny, shrimplike critters known as krill.

Strong northwest winds have been pushing up cold, nutrient-rich waters from the ocean bottom – a phenomenon known as upwelling. That has fueled blooms of phytoplankton that have led to an explosion of krill, the main food source of blue and humpback whales.

"The season overall has been pretty exceptional and we're not done," said Nancy Black, a marine biologist with Monterey Bay Whale Watch, which offers bay cruises twice daily.

The abundance of whales has been a boon to boat tour operators in Monterey Bay, whose deep underwater canyon makes it one of the best places to see whales, dolphins and other marine life.

"The word is out right now. If you want to see a whale or blue whale or several species of whale, now's the time to go for sure," said Ken Stagnaro, co-owner, Santa Cruz Whale Watching, who estimates business has doubled this year over last year.

But the rebound in whale populations has led to a new problem: more collisions with the giant cargo ships heading in and out of San Francisco Bay, one of the world's busiest ports, experts say.

"When a ship strikes a whale, it's usually not a good outcome. Often times the vertebrae are broken and the whale dies," said Maria Brown, superintendent of the Gulf of the Farallones National Marine Sanctuary.

Federal officials are working with conservation groups and the shipping industry on a plan to help protect the whales around San Francisco Bay. They want to reroute ship traffic and improve tracking of whales to reduce collisions.

Conservationists want to ensure that future generations get a chance to see the world's largest animals.

"When you see a whale in the wild, it's a life changing experience," said Maureen Gilbert, an on-board naturalist for Santa Cruz Whale Watching. "You're never the same person after you've had that kind of encounter with a wild animal."

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  • A Humpback whale jumps in the surface of the Pacific Ocean at the Uramba Bahia Malaga natural park in Colombia, on July 16, 2013. Humpback whales (Megaptera novaeangliae) migrate annually from the Antarctic Peninsula to peek into the Colombian Pacific Ocean coast, with an approximate distance of 8,500 km, to give birth and nurse their young. Humpback whales have a life cycle of 50 years or so and is about 18 meters. AFP PHOTO/Luis ROBAYO

  • A Humpback whale jumps in the surface of the Pacific Ocean at the Uramba Bahia Malaga natural park in Colombia, on July 16, 2013. Humpback whales (Megaptera novaeangliae) migrate annually from the Antarctic Peninsula to peek into the Colombian Pacific Ocean coast, with an approximate distance of 8,500 km, to give birth and nurse their young. Humpback whales have a life cycle of 50 years or so and is about 18 meters. AFP PHOTO/Luis ROBAYO

  • A Humpback whale jumps in the surface of the Pacific Ocean at the Uramba Bahia Malaga natural park in Colombia, on July 16, 2013. Humpback whales (Megaptera novaeangliae) migrate annually from the Antarctic Peninsula to peek into the Colombian Pacific Ocean coast, with an approximate distance of 8,500 km, to give birth and nurse their young. Humpback whales have a life cycle of 50 years or so and are about 18 meters long. AFP PHOTO/Luis ROBAYO

  • A Humpback whale jumps in the surface of the Pacific Ocean at the Uramba Bahia Malaga natural park in Colombia, on July 16, 2013. Humpback whales (Megaptera novaeangliae) migrate annually from the Antarctic Peninsula to peek into the Colombian Pacific Ocean coast, with an approximate distance of 8,500 km, to give birth and nurse their young. Humpback whales have a life cycle of 50 years or so and are about 18 meters long. AFP PHOTO/Luis ROBAYO

  • NUUK, GREENLAND - JULY 27: Boats follow a whale as it swims in the water on July 27, 2013 in Nuuk, Greenland. (Photo by Joe Raedle/Getty Images)

  • A whale jumps to the surface off the coast of Libreville in Gabon on August 19, 2013. AFP PHOTO / STEPHANE BERRY

  • A Southern Right Whale breaches on September 5, 2013 in Hermanus, which has become known as a mecca for whale watching. During the southern hemisphere winter months (June - October) the Southern Right Whales migrate to the coastal waters of South Africa, with in excess of 100 whales known to be in the Hermanus area. Whilst in the area, the whales can be seen with their young as they come to Walker Bay to calve and mate. AFP PHOTO / ALEXANDER JOE

  • A Southern Right Whale breaches on September 5, 2013 in Hermanus, which has become known as a mecca for whale watching. During the southern hemisphere winter months (June - October) the Southern Right Whales migrate to the coastal waters of South Africa, with in excess of 100 whales known to be in the Hermanus area. Whilst in the area, the whales can be seen with their young as they come to Walker Bay to calve and mate. AFP PHOTO / ALEXANDER JOE

  • A humpback whale tail breaches off Sydney Heads at the beginning of whale watching season during a Manly Whale Watching tour on June 23, 2011 in Sydney, Australia. (Photo by Cameron Spencer/Getty Images)

  • A humpback whale emerges from the surface of the Pacific Ocean at the Uramba Bahia Malaga natural park in Colombia, on July 22, 2011. (LUIS ROBAYO/AFP/Getty Images)

  • A humpback whale is seen breaching outside of Sydney Heads at the beginning of whale watching season during a Manly Whale Watching tour on June 23, 2011 in Sydney, Australia.

  • In this photo taken July 21, 2011, a baby gray whale is seen with its mother in the Klamath River in Klamath, Calif.

  • An 8.5 metre-long juvenile humpback whale remains stranded on Anaconda beach in La Paloma, department of Rocha, in southeastern Uruguay, on January 27, 2011. AFP

  • A humpback whale is seen breaching outside of Sydney Heads at the beginning of whale watching season during a Manly Whale Watching tour on June 23, 2011 in Sydney, Australia. (Photo by Cameron Spencer/Getty Images)

  • The tail of a humpback whale emerges from the surface of the Pacific Ocean at the Uramba Bahia Malaga natural park in Colombia, on July 22, 2011. (LUIS ROBAYO/AFP/Getty Images)

  • A franco-austral whale surfaces off the coast of Antoniopolis, in the Uruguayan department of Rocha, 220 km east of Montevideo, on September 22, 2012 during the migration to the south. AFP PHOTO/Pablo PORCIUNCULA

  • A franco-austral whale surfaces off the coast of Antoniopolis, in the Uruguayan department of Rocha, 220 km east of Montevideo, on September 22, 2012 during the migration to the south. AFP PHOTO/Pablo PORCIUNCULA

  • A Franco-austral whale surfaces off the coast of Arachania, Rocha, 225 km east of Montevideo, Uruguay, on September 21, 2012 during the migration to the south. AFP PHOTO/Pablo PORCIUNCULA

  • Watch As Whale Jumps Out Of Water And Bumps Canoe

    A couple canoeing in Maui film the moment when a breaching whale his their canoe while paddling out in the ocean.