Ashley McKellar was last seen at a home in the Lake Macquarie suburb of Bolton Point at about 8.30am yesterday.
Police believe the 43-year-old may have launched his boat from lake access at Bolton Point at around 10.30am yesterday.
Rescue teams have searched the lake and are now searching offshore from the lake access point at Swansea up to Anna Bay – an area stretching some 70 kilometres.
The Marine Area Command, the Australian Maritime Safety Authority and Westpac Rescue Helicopter Service are all assisting police in the search.
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Police are calling on the public to come forward with any information they may have about the missing man.
McKellar is described as being of Caucasian appearance, about 185cm tall with a medium build, has short brown hair and wears dark-rimmed glasses.
His boat is a 4.8-metre Telewater aluminium runabout with registration plates VK844N.