A woman driving on the San Mateo-Hayward Bridge pulled to the side of the span, exited her car and jumped into the Bay on Tuesday afternoon, only to swim to shallow water, authorities said.

Yen Hoanj Le, of Hayward, who is in her 20s, was unharmed and officials had no idea why she jumped about a half-mile west of the Hayward tollbooth.

A driver on the San Mateo Bridge noticed the woman pull to the side of the span at 1 p.m. and called police, said Joseph Ford, a civilian search and rescue specialist with the U.S. Coast Guard. Officials from the Coast Guard, California Highway Patrol and Foster City Fire Department sent helicopters, ambulances and patrol cars to respond, he said.

The woman was able to swim to water that was only chest deep, and a ladder was lowered to pull her out of the Bay, Ford said.