Officials say a large oil spill in Westbrook has been contained, but the exact source is still being investigated.

A resident running nearby noticed the smell of oil and a sheen on the Presumpscot River around 8:20 a.m. Friday.

Fire Chief Steve Sloan said the source of the leak isn’t known, but it got into the river through the storm drain system.

An official with the Maine Department of Environmental Protection was going door-to-door asking neighbors if they had a leaking oil tank or pipe in their basements.

A large boom was placed in the river but removed later in the day once the spill was contained.