In Norway, cyanobacterial blooms occur frequently in lakes used for drinking water and recreational use. The associated toxins that have been detected are microcystins and anatoxin-a. About 88 % of the Norwegian population is served with drinking water produced from surface waters and it is obvious that cyanobacterial blooms in potable waters can pose a human health threat. Several eutrofic Norwegian lakes are monitored regularly. There is no national legislation on toxic cyanobacteria in Norway and the Norwegian drinking water regulations do not require water works to monitor cyanobacterial toxins in the raw water.