The Southern California port city of Long Beach has reopened a 4-mile stretch of beach closed since midweek, when tar balls from an unknown source washed ashore.
The Fire Department lifted the closure at 8 a.m. Friday but asked that people stay aware while walking on the beach or swimming.
The shoreline was put off-limits Wednesday night when sticky, oily blobs washed ashore. Authorities worried the substance could cause skin irritation or other adverse health effects.
Cleanup crews scooped up about 55 gallons of the stuff from the beach and took samples for study.
Possible sources include last month's spill of thousands gallons of crude oil more than 100 miles to the northwest on the Santa Barbara County coast.
Tar also recently washed up in nearby Manhattan Beach and Ventura County.