Water quality and Cryptosporidium distribution in an upland water supply catchment, Cumbria, UK

Four micro-catchment (MC) areas were identified to represent the main terrain types of a remote, sparsely populated upland valley catchment of 18 km2 in Cumbria, UK. These were improved land with good grazing (IB), steeply sloping land with rough grazing (SG), wet moorland with sparse grazing (WM) and enclosed woodland that excluded livestock and deer (EW). Each MC contained the origin of a small stream that flowed into Swindale Beck, the river draining the valley. The water quality during the 14-month study, as judged by chemical and physical parameters, was excellent, but it could not be regarded as pristine because of the frequent presence of Cryptosporidium oocysts arising from livestock and wild mammal faeces. Oocysts (0·2-5·6 l-1) detected by genus-specific immunofluorescent antibody were found in 32% of 188 water samples tested: ranking order EW 44%, IB 34%, Beck 30%, SG and WM 26%. Similarly, oocysts were identified in 9·5% of 1730 faecal samples. Small wild mammals (28%), calves (15·7%) and lambs (8·1%) were the dominant sources, whereas adult livestock (1·8%) and large wild mammals (4·8%) were less important. Autumn showed the highest occurrence of oocysts for both water and faecal samples. No hydrological controls were found to have a significant impact on the occurrence or concentration of oocysts in the main river or in the MCs, suggesting that their presence is controlled by seasonal changes in pathogen prevalence in the animal reservoir.