HIGHLANDS, Texas (AP) - Floodwaters have inundated at least five highly contaminated toxic waste sites near Houston - and that's raising concerns the pollution there might spread.

The Associated Press has visited the sites - some still only accessible by boat.

The Houston metro area has long been a center of the U.S. petrochemical industry, and is home to more than a dozen Superfund sites.

The Environmental Protection Agency says Superfund sites are among the most contaminated places in the country.

An EPA spokeswoman says agency experts won't begin assessing the damage at the sites until the floodwaters recede.

Among the Superfund sites completely flooded are the San Jacinto River Waste Pits, the site of a 1960s paper mill. Soil there is contaminated with dioxins - toxic chemicals linked to birth defects and cancer.