SAN FRANCISCO, Jan. 11 (Xinhua) -- A woman was bitten by a sea lion when she was swimming in the waters at San Francisco's Aquatic Park in westen U.S. Thursday in the fourth similar attack in about one month, the San Francisco Fire Department (SFFD) said.

The SFFD said in a Facebook post that it "responded to a reported sea lion attack at Aquatic Park. The responding SFFD Units located an adult female who was being cared for by a retired SFFD Paramedic on the shore."

It said the woman suffered a knee injury and a retired paramedic who was also swimming in the same area helped the victim back to shore where she received first-aid care.

An eye-witness said he saw the woman bleeding badly when she got out of the water.

Similar attacks occurred last month when two swimmers were bitten by sea lions in separate incidents.

In another attack on Dec. 15, a male swimmer suffered a "severe bite" on his thigh and was taken to San Francisco General Hospital.

The latest sea lion attack forced the San Francisco Maritime National Historical Park to close the swimming spot for five days.