• Loch Long
The boat had allegedly been taken from its mooring near Ardgartan on Loch Long in Argyll during the night by someone staying at a nearby campsite.
Its owner went up in his helicopter to look for his boat but was forced to ditch in the water at around 9.10am.
The pilot managed to swim ashore, while the aircraft sank. No-one else was on board.
Meanwhile, a member of the public had spotted the motorboat drifting on Loch Long. Investigators found a man "asleep" on board the vessel, which was towed back to shore.
The man, who had been reported missing from a local campsite at around
7am, was arrested in connection with the alleged theft of a boat.
Clyde Coastguard was involved in the search for the missing vessel.
A spokesman said: "We started searching and put teams out but it was spotted by someone else. It had not gone very far.
"The man that owns it owns his own helicopter and went looking for it and ended up ditching into the loch but he managed to get out and swim ashore."
It is not yet known why the helicopter was forced to ditch in the loch.
A Strathclyde Police spokesman said: "At around 7am this morning police received a report that a man was missing from a campsite near Ardgartan.
"It's believed he may have taken a motorboat and gone out on to the loch at around 2am.
"It's believed the pilot of the helicopter was the owner of the boat which had allegedly been taken by the missing man.
"The pilot was not seriously injured and did not require hospital treatment."