The decision to pour heavily contaminated floodwaters from New Orleans (search) streets into Lake Pontchartrain was a difficult one and could pose new environmental problems in the years ahead, the chief of the Environmental Protection Agency said Thursday.

"We were all faced with a difficult choice," EPA Administrator Stephen Johnson said in an interview with The Associated Press. "The choice was, we have to get the water out of New Orleans for the health and safety of the people and we need to put it someplace."

The other option was to pour it into the Mississippi River, where it eventually would move into the Gulf of Mexico, said Johnson. "Our collective judgment was to put it into Lake Pontchartrain (search)."

He said he could not speculate on the possible environmental fallout for the massive freshwater tidal estuary, but the EPA (search) was prepared to "take whatever steps we need to take" to deal with future environmental problems.

Of the watery soup that has engulfed New Orleans, Johnson said: "This water is very unsafe. It's a health hazard."

The first set of samples tested show it has a level of sewage-related bacteria that is at least 10 times higher than acceptable, as well as a surprising amount of lead. Louisiana officials believe it is laced with an assortment of heavy metals, pesticides and toxic chemicals.

Johnston said the EPA is testing for more than 100 chemicals from heavy metals, pesticides, industrial chemicals and PCBs and expects a more definitive word on the makeup of the hazardous brew in the coming days, possibly as early as this weekend.

So far, the EPA tests have been focused in residential areas and in the French Quarter, not the industrial areas where the floodwaters are likely to be more heavily laced with toxic substances, said Johnson.

"We don't know where the lead came from," said Johnson. "The samples that were taken were not near any industrial area." But he noted the city was full of old homes with lead paint and asbestos, which is probably also in the water.

Johnson said the EPA will also examine sediment for lead and other contaminants. If it is also contaminated, the cleanup could include removal of tons of soil and sediment.

"This is a huge area that encompasses three states," Johnson said. "Given the magnitude of this disaster we at this point can't say what the magnitude of the environmental challenges will be."

Johnson said the EPA is also taking air samples and using sophisticated detection systems to determine whether there might have been radiological releases from hospitals or university research facilities. So far no evidence of such releases has been found, he said.

The 630-square-mile Lake Pontchartrain formed some 5,000 years ago by the meandering Mississippi River (search). Many scientists believe it will survive the latest onslaught, although the effects may linger for decades.

Along with the toxic chemicals and sewage, the lake has become saltier. The hurricane poured waves of saltwater into the lake and the recovery effort will increase the salinity even more. Environmentalists worry that could harm the lake's cypress swamps.

This summer an unusually large number of manatees, an endangered species, were spotted on the lake, according to the Lake Pontchartrain Basin Foundation. Well before the hurricane hit, the group urged visitors to its Web site to look out for the mammals, saying we "want their visit to be safe."