This study was conducted in October-November 2024, at Lake Panjang and Lake Lubuk Siam, Siak Hulu District, Kampar Regency, Riau Province. The purpose of this study was to determine the concentration of chlorophyll-a and the carbon absorption potential of phytoplankton based on chlorophyll-a. Samples were collected at three stations in each lake. The main parameters measured were chlorophyll-a …