RALEIGH, N.C. — The city of Raleigh and the state of North Carolina are investigating whether a white sludge found in a Raleigh creek could contaminate the city's main source for drinking water, Falls Lake.

The sludge and algae blooms -- highly unusual for winter -- cover the creek bed that runs behind Raleigh's E.M. Johnson Water Treatment Plant, off of Falls of Neuse Road just past Interstate 540. The creek eventually dumps into Falls Lake.

Raleigh Public Utilities Director Dale Crisp told WRAL that he believes the discharge could be a calcium-based compound that overflowed during recent work at the plant. The compound, he says, is part of a process to reduce chlorine in water, and that the plant has been cited for it in the past.

As for the algae blooms, Crisp speculates that they could be a result of the unseasonably warm winter.

But residents in the area who have watched the water change colors are both worried and frustrated.

"The creek has changed from a babbling brook that looked pretty to -- as you can see -- pretty nasty looking material," said Ron Gregory, of the Sheffield Manor Neighborhood Association.

Raleigh Mayor Charles Meeker is also frustrated by a series of outflow problems at the plant. In 2002, state inspectors looking for signs of aquatic life in the same creek found black sludge, instead. Months later, the city installed a new dechlorination system in the plant. The most recent consultant report indicates the plant is still troubled by toxicity issues killing off aquatic life.

"Obviously, it's completely unacceptable to have any kind of discharge from a city facility that would violate water quality standards," Meeker said.

State water quality inspectors took samples from the creek Monday and expect to have the test results next week.

In 2002, the state fined another utility plant, Raleigh's Wastewater Treatment Plant, more than $80,000, and cited it for overspraying fields with sludge that contaminated several private wells.

The city raised utility rates to cover millions of dollars in improvements at the plant.