A snail species which almost stopped the A34 Newbury bypass being built has died out in the area, according to a wildlife group.
Buglife said no Desmoulin's whorl snails were left on the site they were moved to before the construction of the road.
Matt Shardlow, director of Buglife - The Invertebrate Conservation Trust, told BBC News: "What happened was that the pipes that fed the water the snails needed on the translocation site became silted up; hence, the fen dried out and this is when the snails got into trouble and became extinct.
"The site could sustain the snails but it is a high-maintenance location. It is high maintenance because it is artificially created and unless you keep it going then troubles begin."
A spokesman for the Highways Agency, which maintains the site, said he completely "refuted" the suggestion of mismanagement.
He said: "We have put a lot of time and resources into the site ever since the snails were moved.
"We still go out and monitor that site continuously."
Mr Shardlow said: "We are in the midst of a biodiversity crisis. The loss of Desmoulin's whorl snail on its translocation site is a timely reminder of the fragility of the wildlife around us.
"Quick fixes rarely work. We need our leaders to take a brave choice that will protect natural resources for our descendants."
The Highways Agency spokesman said an inspector would be sent to the site as a matter of "urgency".
The organisation was given permission to move the Vertigo moulinsiana species to a site two miles away from the bypass in 1996.
The spokesman said: "We will get an inspector out to the site as quickly as possible. Investigations will probably start early next week."
The snail is found at 150 to 160 sites around the UK, according to the Biodiversity Action Plan (BAP) reporting scheme. The UK BAP is the Government's response to the Convention on Biological Diversity.
Dr Roger Key, senior invertebrate ecologist for English Nature, said the Desmoulin whorl snail is a "classic boom and bust" species.
He said: "Its numbers fluctuate on individual sites. Elsewhere it goes up and down like a yo-yo. It can go from none to hundreds and thousands in a square metre.
"We found it was more widespread as a result of the new bypass. We thought it was much rarer at the time than it was.
"They are 1.5mm long and live in deep swamp litter, so they are likely to have been under-reported."
In June 1996, environmental groups and local residents failed in a High Court bid to halt construction of the multi-million pound A34 Newbury bypass in order to protect the snail.
Campaigners had contended that construction could not legally take place along the proposed route, and areas where the snail was known to live should be included on the candidate list for preservation under the EC Habitats Directive.
Expressing regret, the judge at the time ruled that it could not be argued that the Government had unlawfully given construction firm Costain the go-ahead for the bypass contract without first properly considering the needs of Desmoulin's whorl snail.
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