Surfer Brent Manion reported seeing a shark shortly after 3 p.m. Monday near the surf line at Beacon's Beach. He said the shark was 8-10 feet long and resembled a great white, according to authorities."It circled around me once real close and then took another circle about 10 feet out," said Manion.He said he did not even have to think twice about what to do next."Luckily, I wasn't as far out as I could have been and was able to get out of the water quick," he said.Encinitas lifeguards told 10News they believe it is a credible sighting based on Manion's description of the shark."He saw the shape of the nose, a dorsal fin and a straight up-and-down tail fin," said Encinitas lifeguards Sgt. Dave Brown.Crews evacuated the immediate area, and then began making announcements via loudspeakers and "face-to-face," advising beachgoers to avoid the surf in the area for the time being, according to Encinitas Marine Safety Capt. Larry Giles.Lifeguards planned to continue issuing the warnings for the remainder of the day.Sightings of great whites off the coast of northern San Diego County are "pretty rare," Giles said.However, one surfer told 10News he has noticed millions of anchovies in the water during the past three nights.Shark expert Suzanne Kohin of the National Oceanic and Atmospheric Administration told 10News that small great whites like the one Manion said he spotted could be in the area to feed on anchovies because great whites are opportunistic feeders.After Monday's sighting, Encinitas lifeguards are asking surfers to stay out of the water from north Moonlight Beach to south Ponto for at least 24 hours.Manion said he is just happy to be standing on the shore far away from the shark."It kind of freaked me out," he said.