ABSTRACT Oil pollution in the waters is one of the factors that affect the abudance of fhytoplankton, especially the diatom. The waters of Lalang Strait, Mengkapan Village, are used as international shipping lanes and industrial areas. The research was conducted in the Waters of Lalang Strait Mengkapan Village, Siak Regency, Riau Province. The research was conducted at 3 stations with differen…