There are only 100 colonies in the world of the freshwater pearl mussel, the cousin of the ubiquitous mollusc found in moules marinieres, and 47 of these are in Britain.
However, the crofters plan to build a hydro-electric generator on land they own in the Scottish Highlands which will drain a nearby river and thereby destroy the habitat of an established pearl mussel colony.
The Loch Poll scheme on the North Lochinver estate, West Sutherland, which was approved last month, has created a schism between environmental groups.
They are divided on whether to oppose or support the plan to provide power to the National Grid which will generate an income of pounds 200,000 over 15 years for the hard-up crofters.
The Scottish Wildlife Trust says the scheme will spell the end for the pearl mussel population, which has been reduced by a third because of poaching.
The group has accused the crofters of "playing dice" with a species which is the focus for global concern and which was supposed to have been given protection under the Wildlife and Countryside Act last year.
However, the crofters argue that the scheme is necessary to protect their fragile community from economic disaster and that they have devised a plan to move the mussel downstream to prevent its demise.
They have already managed to win over Scottish Natural Heritage, which was initially opposed to the scheme, to their side.
Peter Pollard, the river valleys officer for the Scottish Wildlife Trust, says the scheme will have a global impact on freshwater pearl mussels.
He says the colony is significant because it contains juvenile mussels which are capable of reproducing. Other colonies of the pearl mussel, which can live for up to 130 years, contain animals which are too mature to reproduce.
"This development is not the right one. If the river dries up, they will `drown' in the air," he explained.
"If the mussels are moved downstream there is a risk that the population will be wiped out because they are sensitive to change.
"There is an enormous loss of species going on throughout the world. We are the stronghold for these creatures in Europe and should be setting an example by showing other countries that we can protect species."
Scottish Natural Heritage admits there is a threat to the mussels but says plans have now been put in place to limit the danger.
"They will be affected by the scheme to some degree," said a spokesman. "However, the proposals have been changed to take in the effect on the mussels. There are also other colonies of mussels on the estate which will be protected."
John MacKenzie has been a crofter for 21 years and is used to hardship. He is a member of the Assynt crofters board, whose 120 members bought the 21,000-acre estate in a landmark property deal in 1993.
Mr MacKenzie says the electricity scheme will save the community from crisis and that other options such as wind power would cost millions of pounds to set up.
"The fact is that the environmentalists have shown great interest in these animal species," he added. "But they exist because of the ecologically friendly approach of crofting, unlike other forms of farming which destroy the environment.
"The objective is to make this estate, which is mostly rock and water, work for the community. Far from being environmental philistines we are attempting to safeguard the environment."Reuse content