THE OCCURRENCE OF GONYOSTOMUM-SEMEN (EHR) DIESING IN FINNISH LAKES

Since the early nineteen-eighties swimmers have complained of the nuisance effect of Gonyostomum semen in Finnish lakes. This alga causes an unpleasant slimy coating on the skin after swimming. Although it was first identified in Finland in 1894, the first complaints concerning G. semen were reported to the Finnish water authorities in 1978. During the period 1978-1989 a total of 110 water samples were qualitatively microscoped for G. semen. According to the results the alga seems to have spread from the south-eastern part of Finland throughout the southern part of the country and northwards almost to the Arctic circle. 139 quantitative samples from monitored lakes were also analysed. The alga seems to prefer dystrophic and eutrophic conditions.