DENNIS (CBS) – Crews are searching for a missing swimmer in Scargo Lake on Cape Cod. Dennis Police say they received a report just before 4 p.m. Tuesday.

“Someone saw or heard somebody yelling for help,” said Dennis Fire Chief Mark Dellner. “There was a gentleman in the water just down to our left on the west side of the pond, and they saw him go down and not come back up.”

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State and local police, fire, the dive team and others responded to the lake.

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Dive teams search for reported missing swimmer in Scargo Lake in Dennis (WBZ-TV)

The swimmer is described as a middle aged man who witnesses say was swimming but appeared to be laboring, and went under.

“Based on several witness reports we think there’s an 80 percent chance that there’s somebody still in the water,” Chief Dellner said late Tuesday afternoon. “Right now the State Police are in the air looking from above, we had a drone in the air as well earlier, we currently have a number of divers from the Barnstable dive rescue team in the water.”

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State Police helicopter searches Scargo Lake (WBZ-TV)

Authorities say there are no missing person reports from anybody yet but the witness accounts are enough to prompt this large response, a response that will go on until dusk and beyond.