A police helicopter, divers and rescue boats were spotted in the Balloch area of Loch on Friday evening.
Scottish police have confirmed that divers have been in the water as part of their search for the person.
The Scottish Fire and Rescue Service is also present with two boats and two pumps.
Scottish Police said the incident was ongoing after they were called to a report over concerns over someone in the water at Balloch Country Park.
Trains from Edinburgh: No train can pass through Haymarket due to excess …
A Scottish Police spokesperson said: “Police are working with partners in the emergency services following a report of concerns over a person in the water at Balloch Country Park.”