Abstract: ObjectiveTo investigate the algae pollution of water-supplying system from Yellow River diverting into Taiyuan.Methods Water samples were collected in Wanjiazhai reservoir,the entrance of Huyan water plant,the exit of Huyan water plant and strainerendings.The eutrophic level and algae pollution of the water-supplying system were evaluated through measur ing total nitrogen(TN)concertration,total phosphorus(TP)concertration,chlorophyll-a level(Chla),microcystin-LR(MC-LR)level and total amount of the algal cells.Results Both TN concer tration(3.921 mg/L)and TP concertration(0.45 mg/L)in Wanjiazhai reservoir exceeded the standard Ill(TN1.0 mg/L,TP 0.05 mg/L)of GB3838-2002 《Surface Water Environment Quality Standard》.Chla level was 2.389 μg/L.The amount of algal cells was 150×10⁴/L.The concentration of MC-LR was 0.945 μg/L,lower than the MC-LR limit(1μg/L)of domestic drinking water hygienic guide.The rest indexes of the samples from the entrance of Huyan water plant were the same as Wanjiazhai reservoir,except for TP concentration which was lower than the standardóof GB3838-2002 《Surface Water Environment Quality Standard》.MC-LR level and total amount of the algal cells were obviously lower for the samples of exit of Huyan water plant and strainer endings than those in the entrance of Huyan water plant.Chla was not detected.But TN and TP concentration of samples from strainerendings were higher than that in the exit of Huyan water plant.Conclusion Wanjiazhai reservoir was in eutrophication and algae pollution.TN and TP pollution appeared in the samples from the exit of Huyan water plant and str ainer endings.