GUILDERLAND — Residents of Becker Road, which backs up to the Bozenkill, noticed a sudden change in the level and color of the water on May 18.

The Mastrianas, at 4234 Becker Road, said the water looked like it contained gray sludge, and gave off a stale odor. The water rose up nearly to the brush on the banks,

Tom Brady, the assistant director of environmental health for Albany County, said the health department was notified of the rise on May 21, and investigated the Altamont Wastewater Treatment Plant to see if the sudden rush of water originated there; nothing could be found, he said.

The Bozenkill leads to the Watervliet Reservoir, Guilderland’s major source of drinking water, and William West, Guilderland’s superintendent of water and wastewater management, said the town did not notice a change in the raw water quality or turbidity. The water is filtered; chemicals are added to remove organic and inorganic material; it is put through a carbon filter, and then disinfected, said West. He said, even if something were discharged into the reservoir, it was diluted enough that it did not show up in tests.

West speculated that a collapsed beaver dam could have sent extra water flowing down the creek.