Lakes and quarries are being searched in the hope of finding a Monaghan man missing for 18 years.
Michael Tony Lynch, 55, was reported missing from his home in Clones, Co Monaghan on January 9, 2002.
Mr Walsh, originally from Magheraveely, Co Fermanagh, was last seen three days earlier.
Gardai have now renewed their appeal for information as the 18th anniversary of his disappearance approaches.
Detectives are now probing if Mr Lynch's white Mitsubishi Galant car had been submerged in water in the Clones area.
The first search began on Thursday morning at Gortnawinny Lough.
A garda spokesman said: "The investigation into Mr Lynch’s disappearance is ongoing and to date Mr Lynch and his car - a white Mitsubishi Galant registration number TIL4670 - have not been located.
"The purpose of the planned searches is to establish if Mr Lynch’s vehicle may have been submerged at one of these locations.
"The planned operation will begin on January 2, 2020, and will include the use of a drone which can guide Gardaí and the Civil Defence team to locations of interest in the search.
"Gardaí investigating this missing person case have exhausted a number of leads and at this point are renewing their appeal for information.
"Anyone who may have had sight of this vehicle and/or Mr Lynch since January 6, 2002 is asked to come forward.
"They are also anxious to speak with any landowners who may have noticed a car abandoned on lands or submerged in waters which may fit the description of Mr Lynch’s white Mitsubishi Galant car.
"Those with information are asked to contact Gardaí in Clones on (047) 51028, the Garda confidential line 01-800-666-111 or any Garda Station."
