The beach was closed for the second time in two days Friday after another reported sighting of a dorsal fin in the water.
Mission Beach reopened Saturday after a two-day closure was put into effect due to shark sightings, authorties said.
Authorities did not spot any more sharks overnight Friday, and said that once the advisory expired at 8:15 a.m. the beach would be open to the public.
The beach was closed on Thursday and Friday after two sharks were sighted in the water. The closures were only precautionary, though, said Lt. John Everhart of the San Diego lifeguards.
Thursday at noon, a lifeguard spotted a 10-foot shark about 100 yards off shore, near Tower 15.
The lifeguard was paddling on a board when he saw a dorsal fin about 18 inches long protude from the water, said lifeguard Lt. Nick Lerma.
Based on the size of its dorsal fin, the shark's estimated size was at least 10 feet long, Lerma said.
On Friday morning, longtime surfer, Tom Lochtefeld, spotted another shark near tower 13. He said the dorsal fin was about 14 inches and that the creature did not act aggressively toward him.
Though scientists have not yet determined what type of shark Lochtefeld saw, it potentially could have been a great white shark, as several have recently given birth off the coast of Southern California, said UC Davis shark expert Peter Klimley.
When the sharks give birth, they migrate north, often feeding near beaches, Klimley said.
In each shark sighting swimmers were asked to get out of the water for their own safety. It's unknown whether the sightings were of the same shark.
“I think it’s important to keep it in perspective," said Lerma, "the chances of getting attacked or injured by a shark are infinitesimal compared to chances you take driving to the beach and back home on the freeway.”