The whale, reported Sunday, is one of several to be spotted this month.
Officials from the Gulf of the Farallones National Marine Sanctuary are not releasing the location where the latest whale was sighted, in an effort to keep the curious away, said spokeswoman Mary Jane Schramm.
The appearance is entirely normal, however, and not a cause for concern so long as the whale is not frightened deeper into the Bay where they might have trouble getting out, Schramm said. The whales frequently stop off in the Bay on their migrations between breeding grounds in the south and feeding grounds in the north.
"It's business as usual as long as they're not harassed," Schramm said.
Boaters are instructed not to 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. Separating a calf from its mother would doom it to starvation, officials said.
Collisions between boats and whales can have disastrous impacts for both the whale and the vessel, and could result in legal consequences, according to the marine sanctuary, a division of the National Oceanic and Atmospheric Administration.
Schramm said that many boaters aren't aware of the regulations regarding approaching whales, and that boaters may inadvertently cause the whales harm.
More whale activity in and around San Francisco Bay is expected as gray whales travel near the shore of San Francisco and Tomales Bay, migrating from their breeding grounds near Mexico around 6,000 miles to feeding grounds near Alaska.
"It's like they spend half the year in the bedroom and the other half of the year in the kitchen and pantry," Schramm said.
Gray whales in particular swim close to the shore, and cow-calf pairs sometimes pause in surf zones for the calf to nurse or rest, or when avoiding killer whales.
While not much of a whale is usually visible on the surface, whales can be spotted by their blow, which looks like a puff of smoke about 10 to 15 feet high. Whales will blow several times before diving for three to six minutes, marine sanctuary officials said.
All whales are protected by the Marine Mammal Protection Act and some species, such as humpback and blue whales, are also protected by the Endangered Species Act.
Despite the legal restrictions, Schramm said there are plenty of ways for people to observe whales around San Francisco, as long as whale watchers are with a captain that knows how to navigate near whales, and a naturalist that can explain whale behavior.