Researchers at the University of Hawaii say a huge amount of debris from Japan, swept away in March's tsunami, is moving across the Pacific Ocean.
The researchers predict the first batch of debris, including construction material, cars, trees, roof tops and household items, could hit Hawaii in about two years and reach California's shore in three years.
The University's International Pacific Research Centre, Jan Hafner, says an island of debris has already moved a few hundred kilometres away from the Japanese shore.
He told the Voice of America that strong currents are moving it across the ocean.
He says by the time the debris reaches the U.S. West coast, it will turn into what the scientist calls "the North Pacific garbage patch."
He says batches of that garbage are expected to continue trickling to Hawaii shores for about five more years.
The projections are based on a diagnostic model, which has been developed using realistic data about objects drifting over the ocean surface.