Abstract
Attainment conditions of the water quality standard (COD) in Japanese 113 lakes (197 designated sites) were investigated by using observed COD concentration between 1978 and 1988. Observed concentration in about a half of all designated sites have exceeded the standard value of each site every year. Only 20% of the sites have attained the water quality standard every year. Objective 113 lakes could be classified according to two indices of ‘the ratio of exceeding year in 1978-1988’ and ‘the ratio of observed mean in 1978-1988 to the standard’. Though the attainment conditions throughout Japanese lakes have become better, the decreasing ratio of the autochthonous COD to the allochthonous indicated the emphasis of watershed management.
