Up to 160 divers are taking part in what is thought to be the biggest underwater search operation in the history of the state.
The dive teams are searching the sea around Blackrock Island off the North Mayo Coast, where the Rescue 116 helicopter crashed.
Efforts to locate two missing crew of Rescue 116 will step up a gear this weekend.
A significant dive operation will take place - with over 100 divers traveling to Mayo to aid in the operation.
It is over a month since the Coast Guard helicopter crashed on Blackrock Island.
Captains Dara Fitzpatrick and Mark Duffy have since been recovered and laid to rest however Winchmen Paul Ormsby and Ciaran Smith remain at sea.