Riverkeeper, a regional environmental group, announced yesterday it has sent notices of intent to sue to each of the companies, which all operate on the banks of the long-polluted creek running between north Brooklyn and Queens.

The group accuses the companies of dumping toxic materials and other forms of pollution into the industrialized waterway. Illegal dumping is a violation of the federal Clean Water Act of 1972.

Among the accused companies are Allocco Recycling, a soil and construction-debris recycling company that activists say routinely lets toxic materials fall into the creek, and Marjam Supply Co., a construction supply center accused of dumping trash onto the banks of the creek, all of which get picked up by the tide.

"This is a classic example of an industry that mistreats its waterway," said Riverkeeper investigator Basil Seggos, pointing to debris spilling off Marjam's site during a boat tour along the river yesterday. "It's treating the creek as an open dump," added Riverkeeper Executive Director Alex Matthiessen.

Marjam Vice President Carmen Arguelles said yesterday she had no knowledge of the suit and emphasized that the company takes great pains to ensure debris does not fall into the waterway. "We routinely clean it up," she said.

Other accused polluters include Quality Concrete Corp., a cement plant that activists say discharges liquid cement straight into the water, and Newtown Metal Corp., a metal scrapyard also accused of dumping debris into the creek.

UB Distributors, a beverage distributor, has been accused of routinely dumping soapy dishwater into the creek.

Jim Conklin of Quality Concrete said his company does not pollute the creek. "We're certainly careful about those types of matters," he said. Officials from the other three companies either declined to comment or could not be reached.

Under federal law, the accused polluters have 60 days to change their ways or risk being taken to court by the activist group. If convicted, the companies could face fines of up to $31,000 a day per pollutant, activists said.

The group said the five threatened lawsuits are the first wave of a large-scale push to clean up Newtown Creek, which they said is among the most polluted waterways in the country.

"Our goal is essentially to reclaim, restore and revitalize this creek," said Matthiessen.