SAN DIEGO (CNS) - The U.S. Coast Guard Monday was investigating the death of an 84-year-old woman who fell down some stairs on a whale-watching boat Sunday.

The accident aboard the 100-foot Marietta, a two-deck tour boat operated by San Diego Harbor Excursions, occurred about 11:30 a.m. when the vessel was about 5 miles offshore, Coast Guard Petty Officer 1st Class Henry Dunphy said.

The woman's name was unavailable Monday. She was taken to the pier at the foot of West Broadway and turned over to paramedics, who took her to a hospital where she was declared dead, Dunphy said.

The Coast Guard investigates deaths and injuries onboard vessels for hire, he said.

"We investigate to see if all the correct safety procedures were followed and if there's any recommendations we can make to improve safety on the boat," Dunphy said.

The Marietta is rated for up to 525 people.