Just across the East River from midtown Manhattan's shimmering skyscrapers sits one of the nation's most polluted neighborhoods, fouled by generations of industrial waste, overflow from the city's sewage system and an underground oil leak bigger than the Exxon Valdez spill.

It's easy to see - and smell - the filth in and around Newtown Creek, which runs through an area of working-class homes, warehouses and industrial lots straddling Brooklyn and Queens. The odor of petroleum mixes with the smell of sewage, particularly on rainy days when the city's treatment plants can't handle the volume and municipal pipes send trash and human waste straight into the creek.

Oily, rainbow-slicked water is filled with soda cans, plastic bottles, raw sewage and decaying food. Ditched vehicles are stuck in the mud on the banks. And what was once a creek teeming with fish, surrounded by marshland, is now a dull gray waterway that cannot sustain life.

"It's the byproduct of our society," says environmentalist John Lipscomb of the Riverkeeper clean-water advocacy group. "What was originally a watershed is now a sewage shed."

After generations of neglect, the first, small steps are being taken in a multi-pronged cleanup that could take at least a dozen years and cost hundreds of millions of dollars. But even the most hopeful officials acknowledge the watershed may never be clear of all pollutants.

There was a time when Newtown Creek was the city's industrial mecca. The Rockefellers operated the nation's first modern refineries on its banks in the late 1800s. Others quickly sprang up.

For much of the 20th century, the neighborhood teemed with commercial vessels and factories that made products as varied as fertilizers, chemicals, lumber and glue. Their oil and other hazardous waste was either dumped or leaked into the creek, bit by bit, accumulating at the bottom.

The first sign of the looming ecological disaster came on Oct. 5, 1950, when petroleum gases from the hidden spill seeped into the sewer and caught fire, causing an explosion that blew dozens of manhole covers three stories into the air, shattering windows in hundreds of buildings and ripping a street open. Three people were injured.