The Zerebar Lake is a shallow freshwater lake located in the northwestern Iran. The lake is surrounded by three human activities: agriculture, tourism and dam. The present study aimed to investigate (1) which human activity has the greatest impact on eutrophication of the Zerebar Lake (2) If phytoplankton communities, as the indicator, are correlated with the human activities. Water samples were collected from three selected sites (nearby three human activities) in the Lake every two months, from August 2010 to June 2011. Water variables and parameters of phytoplankton communities (distribution, abundance, biomass and diversity indices) were examined. Agricultural runoff had the main effect on eutrophication of the Lake and the dam deteriorated trophic condition by preventing removal of the nutrients. Although, phytoplankton diversity was affected by nutrients, especially phosphorous, phytoplankton biomass was likely affected by physical parameters, mainly light. The present study suggests that phytoplankton diversity indices are not good indicators for anthropogenic activities around the Lake. However, some phytoplankton genera were more suitable indicators of trophic condition of the lake than others.
