Barecroft Common protected wetlands damaged by M4 survey work
A protected nature reserve was badly damaged by Welsh Government contractors carrying out survey work for a new motorway, a wildlife trust said.
The "substantial" damage to Barecroft Common on Magor Marsh nature reserve was caused when a specialist truck became stuck in deep soil.
Gwent Wildlife Trust said a recovery truck also became stuck and had to be rescued by a third vehicle.
The Welsh Government said it would ensure the field was restored.
"Due to recent heavy rain, a survey vehicle got stuck on the Gwent Levels at the entrance to a field.
Geological ground work
"The survey team will liaise with the Gwent Wildlife Trust and Natural Resources Wales, as necessary, to ensure the field is carefully reinstated at the survey team's cost," a Welsh Government spokesperson said.
The government proposes to build a six-lane M4 motorway south of Newport, which would cut through the wetlands, but a decision on whether to go ahead has not yet been made.
Motorway sub-contractors were attempting to carry out geological ground survey work on Barecroft Common when their vehicle became stuck in the mud.
The first truck, a specialist Unimog vehicle, became bogged down in peaty soil on November 30 and was left there over the weekend, sinking further and causing further damage, the Trust said.
A recovery truck, sent to rescue the Unimog, also became stuck in the peat and a third bigger recovery vehicle had to be brought in, to rescue both the Unimog and the original recovery truck.
Barecroft Common is threatened by what the Trust calls a "hugely damaging" 14-mile route that would carve its way through four nationally protected areas.
The wetlands are home to rare wildlife such as otters, water voles and shrill carder bees, the trust said.