BISMARCK, N.D. — The North Dakota Health Department says a truck spilled more than 4,600 gallons of oilfield wastewater in Williston.

The agency says the produced water spill was the result of an accident on Wednesday by a truck operated by Wind River Oil Services.

Produced water is a mixture of saltwater and oil that can contain drilling chemicals.

State health officials say all but about 200 gallons of the spill had been recovered by Friday afternoon. They say an undetermined amount flowed off the accident site into a drainage and wetland.

Health Department officials say they are monitoring the cleanup effort.