PORT MANATEE – An estimated 900 gallons of spilled oil was discovered in Tampa Bay at dawn on Monday morning as it was being loaded from a barge berthed at Port Manatee to a pipeline bound for a storage tank.

The spill was halted on Monday morning in a dockside valve pit where oil is off-loaded, said Mel Klein, a spokesman for Florida Power & Light, which was shipping the Number 6 fuel oil to its Manatee Energy Center in Parrish.

By dusk, about 400 gallons remained in Tampa Bay, he said. Oil also was reported in the shipping channel. Klein said it was unclear whether the winds and tides had swept any oil into the Gulf of Mexico.

By Monday evening, it was too early to tell whether the spilled oil had drifted to seagrass beds in nearby Bishop Harbor and Cockroach Bay, said Chris Rossbach, emergency response manager for the Tampa office of the Florida Department of Environmental Protection.

The cause of the spill has yet to be determined. No injuries were reported.

The spill, which occurred just east of a man-made bird nesting island known as Manbirdy Island, is small compared to the 330,000 gallons of Number 6 fuel oil and 32,000 gallons of jet, diesel fuel and gasoline spilled in 1993 when three barges collided in Tampa Bay, Rossbach said.

"Any amount is serious for all of us," Klein said, adding that the estimate could change as more information is gathered.

The U.S. Coast Guard is monitoring cleanup operations, which included trapping some of the spilled oil with 2,200 feet of absorbent floating containment booms and vacuuming it from the surface, Lt. Commander Steven Lang said.