Four people were rescued after a speedboat sank near Bangor Pier.
The 17-foot vessel had already began sinking when the RNLI at Beaumaris launched its inshore lifeboat at around 1.15pm on Sunday afternoon.
By the time the crew arrived, only the bow of the speedboat was above the water and the crew had been rescued by passing craft and taken back to shore.
Two RNLI crew members went ashore to check on the crew members until the mobile coastguard team from Bangor took over.
Efforts to move the sinking boat to avoid a navigational hazard ended when it suddenly disappeared beneath the waves, sinking in around nine metres of water just inside the channel, as the lifeboat crew were preparing a long tow.
The coastguard was informed of the sunken wreck's exact position, before floating debris was collected from another vessel and taken to the mobile coastguard team.
An RNLI Beaumaris spokesperson said: "The swift reporting of the problem by passing craft to the Coastguard meant our volunteer lifeboat crew were able to reach the vessel quickly, assess the situation and take the best course of action."
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