Hazardous materials teams from Loudoun and Fairfax counties worked for several hours yesterday to contain a slimy green substance that coated the southern part of a small lake in Sugarland Run.

Test results confirmed that the substance in Willow Lake was not harmful, but it had not been determined what the strong-smelling substance was by Friday afternoon. Mary Maguire, spokesman for Loudoun County Fire and Rescue Services, said it looked like "pond scum."

Fire and rescue officials received word of the substance about 9 p.m. Thursday from a resident complaining of a pungent odor coming from the lake. A sample of lake water was taken to a laboratory for testing.

Friday morning, officials received calls from a community swimming pool just beyond the north end of the lake about several children experiencing lightheadedness and scratchy throats. Fire and rescue officials dispatched a hazardous materials team just before 11 a.m.

Ten children were checked out by paramedics. Officials said they do not know whether the children's symptoms and the unknown substance in the lake were connected. The symptoms had subsided by 1 p.m.

The hazardous materials team placed white booms to absorb the substance and contain it to a small portion of the lake. GEC Environmental Contracting, of Lovettsville, used a vacuum truck to remove it.