In present study, algal groups which are used as indicator to trophic and pollution status of Duhok lake. Data that applied for Nygaard’s indices, dominant genus scores, Chlorophyll a and Palmer’s index of pollution, were collected from only previous study happened for Duhok lake during 2002. Total 250 algal taxa which have classified into 6 taxonomic groups were identified. Diatoms members constituted the dominant phytoplankton group in terms of species number, out of 115 identified taxa of diatoms; only seven centric taxa were identified. The Nygaard’s compound index value and composition of phytoplankton indicate that the trophic state of Duhok Dam Lake was eutrophic. The trophic state indices of Myxophycean and Chlorophycean in this survey is indicating Eutrophic nature of lake water and the trophic state indices of Diatoms and Euglenophycean indicate oligotrophic nature of water. As a result of dominant genus scores was (5.7), the lake has a mesotrophic-eutrophic character according to trophic level, in addition, the water quality of Lake Duhok was moderate and moderate polluted in 2002. According to concentration of Chlorophyll-a never fell below (15µg- chl a l-1) and was eutrophic status. The most pollution tolerant species of Euglena, Phacus, Phormidium, Oscillatoria, Scenedesmus, Pandorina, Chlamydomonas, Closterium and Nitzschia identified in lake. These genus are tolerant to pollution depending to Palmer (1969). This communities of algae indicate to that reservoir was highly polluted by organic matter. The total score of Algal genus pollution index was 37 in Duhok lake that indicates to confirm high organic pollution and was eutrophic state.