North Baray reservoir, which was established in the year 1200 around the Angkor region of Cambodia, was abandoned for several hundred years after water leakage. Subsequently, secondary forest developed in this area. However, in connection with city planning, this area was re-inundated in 2008. Dissolved organic matter, derived from the dead trees in this area, is suspected to cause water pollution. This study shows the changes in the distribution of aquatic vegetation in the North Baray reservoir in relation to environmental factors such as topography and water quality.
　A phytosociological survey of aquatic plants was conducted in 140 randomly set quadrats on the west side of the North Baray reservoir during the rainy season of 2014 and 2016. We measured water depth, EC, pH, DO, and chlorophyll concentration by a multi-parameter water quality meter and portable pH meter.
　A total of 18 and 27 aquatic plant species were identified in 2014 and 2016, respectively. The aquatic vegetation of the North Baray reservoir was classified into eight types by TWINSPAN. CCA suggested that the distribution of aquatic vegetation is affected by the water depth, EC, chlorophyll concentration, DO, species density as well as surface and bottom coverage of water. The area of dead trees and bushes remarkably decreased from 2014 to 2016. These changes in topography decreased the submerged and free-floating plants-dominated community, but increased the floating leaved plants-dominated community. These were accompanied by reduction in the chlorophyll concentration and DO in the water.