OCCURRENCE OF CRYPTOSPORIDIUM OOCYSTS AND GIARDIA CYSTS IN THE RIVER MEUSE AND REMOVAL IN THE BIESBOSCH RESERVOIRS

The first results from an ongoing research project, carried out by the Water Storage Corporation Brabantse Biesbosch and several partners, a re presented. The main research objectives are to gather information o n the occurrence of Cryptosporidium and Giardia in the raw-water sourc e (River Meuse), to determine the removal of the parasites in the Bies bosch reservoirs and to detect correlations between water-quality para meters and (oo)cyst densities. Cryptosporidium and Giardia densities i n the Meuse were found to peak in winter, In the last of the three int erconnected reservoirs (oo)cysts were intermittently present throughou t the year. Giardia levels were higher than Cryptosporidium levels, wh ile both were lower than reported in most other surveys. It is conclud ed that water storage in reservoirs with long retention times markedly reduces Giardia and Cryptosporidium concentrations.