Natalie Wood's death is now officially "undetermined", sources confirm.

The actress was found dead during a yacht trip in 1981 off the coast of California with her husband Robert Wagner and her co-star Christopher Walken from the 1983 released film Brainstorm. She passed away at the age of 43.

The inquiry into her case was reopened last year by Los Angeles authorities.

TMZ reports that the L.A. County Coroner's office filed papers to change the type of death from "accident" to "undetermined" last month.

According to the website, investigators are finding it difficult to prove that Natalie's death was accidental because bruises on her body were inconsistent with that conclusion. She did die from drowning, but detectives are not sure how she got into the water.

Wood is best known for her roles in West Side Story and Rebel Without a Cause. She received three Oscar nominations during her career.