M4 relief road plan is 'government-sponsored ecocide'
Plans to build a £1.1bn M4 relief road through the Gwent Levels have been described as "government sponsored ecocide".
Nature presenter Iolo Williams said species including otters, water voles, bats, dormice and rare beetles would be affected by the motorway.
The Welsh Government said mitigation works would include new mammal tunnels.
But in a statement to the public inquiry in Newport Mr Williams said these were "nothing short of a joke".
In the written submission the BBC naturalist accused the Welsh Government of sponsoring "ecocide" - the extensive destruction of non-human life.
The Welsh Government's preferred route - known as the "black route" - cuts across the Gwent Levels and four sites of special scientific interest (SSSI).
In evidence submitted to the inquiry on Wednesday, Mr Williams argued the levels were "one of the jewels in the crown of Wales" and the "green lung of Newport".
Destroying them would be "madness" and cause "unprecedented" damage, he wrote as well as destroying history.
"I despair, I really do despair. It genuinely doesn't make sense," he added.
"The Gwent Levels are a fantastic place to visit, but to hear and see motorway traffic going past, and less wildlife, would break my heart."
The Welsh Government has said a 14-mile six-lane motorway will relieve congestion between the current M4 junction 23A at Magor to junction 29 near Castleton.
Proposals to protect wildlife include creating tunnels and bridges, reed beds, and a bat barn - as well as moving large numbers of dormice to Bristol Zoo during construction.
However, Gwent Wildlife Trust has argued these mitigation proposals are "grossly inadequate".
On day 19 of the inquiry, conservationist Prof John Altringham said the motorway had the potential to do "considerable damage" to bats.
He said bats could be killed crossing the motorway, tunnels were "too small" and plans to build them boxes as alternative homes for lost habitat were "simply eviction".
The Welsh Government said the proposed mitigation measures would reduce the impact of the road on bats to "slight".
An overpass on the A487 Portmadog bypass saw 97% of bats use it safely in 2012, it said.
M4 relief road key points:
The Welsh Government wants to build a £1.1bn six-lane motorway to the south of Newport.
The 14.23m (23km) highway will be between the current M4 junction 23A at Magor to junction 29 near Castleton.
The Welsh Government plans to begin construction in 2018 and open the new road in 2021.
It said the current M4 around Newport opened in 1967 but "does not meet modern motorway design standards".
Environmental campaigners and local residents claim the scheme will devastate the ancient marshlands of the Gwent Levels and four sites of special scientific interest.
There have been 335 formal objections, compared to 210 letters of support.
A public inquiry is expected to last five months.