Bay boaters should make sure to be on high alert today, after multiple sightings of whales near the San Francisco shore.

According to CBS 5, two whales were spotted swimming between Alcatraz and Angel Island on Monday. CBS's chopper managed to get footage of the duo as they swam "side by side just off Crissy Field...heading out towards the Golden Gate Bridge."

SFist editor Jay Barmann says he also saw four whales on Sunday afternoon, "just inside the Golden Gate."

Barmann was on a boat when his group spotted "a pod of four," he says. "We thought they were swimming out, but then we lost them."

Gulf of the Farallones National Marine Sanctuary spokesperson Mary Jane Schramm says that whales make a habit of "stopping off in the Bay on their migrations between breeding grounds in the south and feeding grounds in the north," and that as long as they're not heading deeper into the Bay where they might get stuck, there's no cause for concern.

Gray whales in particular, Schramm says, keep close to the shore and mother and calf pairs will often take pit stops for the calf to nurse or rest.

"It's business as usual as long as they're not harassed," Schramm says, warning boaters that they must not "get within 300 feet of a whale, cut across a whale's path, make sudden speed or directional changes around a whale, or get between a whale cow and her calf."

Update: More from Tuesday via a photographer on the Golden Gate Bridge.