Lifeguards warned beachgoers not to swim in waters off Kailua Beach yesterday after swimmers complained of an oily substance in the ocean.

The substance was first reported at 12:20 p.m., said Bryan Cheplic, spokesman for the city Emergency Services Department.

About 25 people complained to lifeguards after coming in contact with a slippery substance that tasted like oil, Cheplic said. A sheen of about 150 yards by 50 yards was seen off the Kailua Beach Park boat-ramp area.

The state Department of Land and Natural Resources and the Coast Guard were contacted.