Green algae in guts of L. crystallinus (Image by Samantha Hill)
Rare (IUCN Red Data Book 1992)
Not enough is known about the biology of L. crystallinus to classify specific threats.
L. crystallinus was once abundant in the Norfolk Broads but has not been found there since the 1970s. In 2007 it was believed to occur in only 4 sites in the UK.
The population decline may, however, be less severe than perceived. New sampling methods have revealed its presence in 16 new sites in southern England (Hill et al. 2007).
Hartikainen et al. (2007) have increased the number of rivers known to harbour L. crystallinus to >20. These studies indicate that the species is more widely distributed than previously appreciated.
Management consists of retaining habitat complexity and protecting existing sites known to contain permanent populations.
Clearing of wood and plant matter is discouraged as this provides important habitat for attached colonies.