Azhar, Ratih2013-04-042013-04-042013-04-04sumarnihttp://repository.unri.ac.id:80/handle/123456789/2760This research was conducted in August 2011, located in the waters of the Lalang village, District of Siak, Riau Province. This research was aimed to determine the oil consentration, the abundance of diatoms and the relationships between oil consentration with abundance of diatoms (Bacillariophyta) in the waters around the Lalang Village. The method used in this study is a survey method. Based on the results, the highest average value of oil consentration was obtained at Station III (0.615 ppm). It’s different from Station I which has a lowest average rating of oil consentration (0.269 ppm). Six diatoms spesies were recorded in namely in the waters of the Lalang Village, ie. Chaetoceros cinctum, Coscinodiscus lineatus, Nitzschia seriata, Planktoniella sol, Rhizosolenia alata, and Skeletonema costatum. Where Nitzschia seriata species has an average number of the highest abundance (3,000 ind / l) compared to other species and the most commonly encountered at each station. Average abundance of diatom species in each station (8240 ind / l). The relationship between oil consentrasion and abudance diatoms shown that a negative relationship as expressed in formulation y = -5992 x + 4954 with a coefficient of determination (R2) = 0.827 and the correlation coefficient (r) = 0.909. So that, the increasing of oil consentration will be declining the diatoms abudance in the water Lalang Village.otherOil consentrasionDiatomsLalang Villagestudent Paper Post Degree