SAN FRANCISCO, Dec. 30 (Xinhua) -- A surfer was injured after he was bitten on the foot by a shark Saturday off the coast northwest of San Francisco in the northwest Pacific United States, the National Park Service (NPS) said on its Twitter account.

Officials at Point Reyes National Seashore said that a shark attacked the surfer near the mouth of Drakes Estero, an estuary off the coast of Marin County northwest of San Fracisco.

The National Park Service said that the water in the area is off limits to the public.

"A surfer was bitten on the foot by a shark today near the mouth of Drakes Estero. Going into the water is CLOSED until further notice," Point Reyes NPS tweeted.

Saturday's incident was the third attack on humans by marine animals in less than a month.

Earlier this month, two swimmers were bitten by sea lions in two separate incidents, in which one of the swimmer suffered "a very serious bite" in the groin area.

The attack led to the closure of the Aquatic Park Cove in San Francisco for several days. The Cove is a favorite spot for many dedicated swimmers in the city.