Blue-green algae is predominant in Dianshan Lake

Dianshan Lake is the largest lake in the Shanghai suburbs and also one of the most important fresh water sources for Shanghai. To investigate the growth and predominant genera of algae in the lake, water samples were collected during the summer and autumn of 2002. The number of algae cells was counted, each algae genus was identified, and the percentage of each major taxa was calculated. The number of algae cells was affected with alternation of seasons and ranged between 2.27 × 106 l− 1 and 4.24 × 106 l− 1. The percentage of Cyanophyta and Chlorophyta ranged from 20 to about 73% and 21 to about 65%, respectively. The growth and population of Bacillariophyta and Euglenophyta were less than 20% during the sampling period. The change of Cyanophyta population resembled that of the total algae temporally. Cyanophyta reached 50% in the blue-green algae population; the impending water bloom posed a risk to health. Blue-green algae were the dominant algae in Dianshan Lake during the summer and autumn.