If you had asked any British naturalist 100 years ago to identify a common or abundant freshwater river mussel, the chance are that he or she would have identified the Freshwater Pearl Mussel Margaritifera margaritifera. Ask the same question today and you would get a very different answer. In every part of its range, the once common Freshwater Pearl Mussel is now highly threatened and endangered. So, what brought about this dramatic change and why should we care?