A group of about 20 sharks should make Northern California beachgoers take a second's pause.
Almost two dozen great whites were spotted by the U.S. Coast Guard Oct. 16 off Pacifica, a coastal community near San Francisco.
The sharks were mostly between 10 and 15 feet long, which is about half the length great whites can grow. But some were at least 18 feet.
Days before the cluster was found, a shark was seen attacking a seal or sea lion near Alcatraz.
A shark conservationist told KTVU the rare sighting is "... actually a sign that maybe the San Francisco Bay is getting a little healthier, that you have top predators like white sharks coming in."
Now, experts aren't saying these sharks are dangerous enough to prevent residents from getting in the water.
"It's not a school. It's not a swarm. It's not a group of vicious man-eating sharks. They're out there preying on their normal prey, which is seals and sea lions," the director of a shark conservation group told KPIX.
They are, however, advocating for a bit of caution. One expert told KTVU, if you're afraid of sharks, wait for the end of the year, when they move deeper into the ocean.
See other recent shark sightings and attacks:
Recent shark sightings, attacks
The US Coast Guard spotted 20 sharks off the coast of Pacifica, a community near San Francisco
In this photo taken, Tuesday, July 7, 2015, a sign warns visitors about sharks along the Cape Hatteras National Seashore in Cape Hatteras, N.C. ?In a 28-day span, eight people have been bitten by sharks in N.C., with three of the attacks happening on the barrier islands of the Outer Banks. (AP Photo/Tamara Lush)
Map locates Outer Banks, N.C.; 2c x 3 inches; 96.3 mm x 76 mm;
Vacationers sit in chairs in the surf in Oak Island, N.C., Monday, June 15, 2015. A 12-year-old girl from Asheboro lost part of her arm and suffered a leg injury, and a 16-year-old boy from Colorado lost his left arm about an hour later and 2 miles away in two separate shark attacks late Sunday afternoon. (AP Photo/Chuck Burton)
Children play on a shark net at Little Manly Cove as shark experts assess cutting-edge technologies to counter attacks at a summit in Sydney on September 29, 2015, following an 'unprecedented' spate of encounters in eastern Australia this year that has left one dead and seven injured. Australia is home to one of the world's highest incidents of shark attacks, with the two-day summit, which include researchers from the US and South Africa, organised in part to address community fears after the recent incidents on the north coast of the most populous state New South Wales. AFP PHOTO / William WEST (Photo credit should read WILLIAM WEST/AFP/Getty Images)
SYDNEY, AUSTRALIA - JULY 21: Australian surfer Mick Fanning speaks to the media during a press conference at All Sorts Sports Factory on July 21, 2015 in Sydney, Australia. Fanning escaped a shark attack in Jeffreys Bay, South Africa during the 2015 J-Bay Open. (Photo by Mark Kolbe/Getty Images)
Two teenagers sit next to a surfboard reading 'For you my Titi' during a march in tribute to a 13-year-old boy attacked and killed by a shark three days ago, on April 15, 2015 in Saint-Paul on the western coast of the French Indian Ocean island of La Reunion. It was the 16th shark attack on the island since 2011 and the seventh loss of life. AFP PHOTO / RICHARD BOUHET (Photo credit should read RICHARD BOUHET/AFP/Getty Images)
BALLINA, AUSTRALIA - FEBRUARY 10: A lifeguard patrols Shelly Beach on February 10, 2015 in Ballina, Australia. Beaches in northern NSW remain closed after Tadashi Nakahara, 41, was killed on Monday morning when he was bitten by a large shark at Shelly Beach. (Photo by Chris Hyde/Getty Images)