The coracles are being used to guide the giant stone downstream to Milford Haven.
A large crane had to be used to manouevre the Preseli bluestone into two specially-designed river coracles in west Wales before Saturday night's high tide.
A JCB had to be tied to the crane to ensure it did not topple into the Cleddau River at Black Mill Pool.
Menter Preseli, which is organising the transport of the bluestone from Preseli to Stonehenge, said the stone was sucessfully taken by the tide along the Cleddau River as far as Lawrenny, according to plan.
The operation had been postponed 24 hours earlier on Friday after the stone failed to slide into position, mid-stream in the River Cleddau.
The coracles are being used to guide the giant stone downstream to Milford Haven.
Earlier in the week, a 24-hour security watch was mounted on the stone.
The decision followed the 'theft' of the sled used to carry the Preseli bluestone rock - from underneath the stone itself.
The team hauling the stone on its 240-mile journey arrived on Bank Holiday Monday at Castle Bridge Woods in west Wales to find the sled had vanished.
The operation still managed to finish on time that day.
The team of volunteers managed just one mile on their first day - a third of the hoped for target.
Then a lack of volunteers caused another day of stone pulling to be called off.
The ambitious project aims to follow in the footsteps of the ancient builders of the famous monument on Salisbury Plain, Wiltshire.
Neolithic
The plan is to drag the stone at weekends and reach Stonehenge in September.
The trek will include taking the stone across the Bristol Channel on the route, which may have been used by Neolithic workers.
Some experts say the inner ring of the monument is made of bluestones, which were carved out of the Welsh mountains before being heaved on sledges and boats to the Wiltshire site.
It will then be dragged the final 26 miles to the Stonehenge site.
The National Lottery funded Millennium Stone project will involve up to 300 volunteers.
It is being funded by a £100,000 Heritage Lottery grant.
Related to this story:
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Bronze Age skeleton is reburied at caves
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Stonehenge haul grinds to a halt
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Mammoth Stonehenge trek starts
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