In May (the dry season) , August (the wet season) and November (the normal season) 2009, water samples were collected from a number of rivers, including Ji Canal, Chaobai New River, Yongding New River, Jinzhong River, Beitang Channel, Heizhu River, Haihe River, Dagu Sewage Channel, Duliujian River, Qingjinghuang Drain, Ziya New River and North Canal in Tianjin and analyzed for monitoring of water quality. Principal component analysis was conducted of the monitoring data. On such a basis, a water quality evaluation index system was established, using water quality identification indices to evaluate water quality. Results show that the evaluation combining PCA with the water quality identification indices is objective and reliable. The temporal variation of the water quality on the whole reveals that it is the worst in the dry season, when the water quality of 58. 3% of the rivers were worse than Grade V of standard for surface water and some even turned to blackish. However, the water quality turned relatively good in the wet season ( August). In light of the comprehensive water quality identification indices, the rivers south to the Haihe River were more seriously polluted, especially with ammonia nitrogen, which was followed by BOD5 , CODMn and TP. The pollution was of the organic and eu-trophicating type.%于2009年5月(枯水期)、8月(丰水期)、11月(平水期)对天津地区蓟运河、潮白新河、永定新河、金钟河、北塘排污河、黑猪河、海河、大沽排污河、独流减河、青静黄排水渠、子牙新河和北排水河12条主要河流的水质进行监测,并对监测数据进行主成分分析,构建水质评价指标体系,采用水质标识指数进行水质评价.结果表明,主成分分析与水质标识指数相结合的评价方法客观可靠.从时间分布来看,枯水期水质最差,58.3％的河流为劣V类水质,部分河流已经黑臭,8月水质较好.从综合水质标识指数来看,海河以南河流污染较为严重.该地区河流NH3-N污染最为严重,其次是BOD5、CODMn和TP,属于有机型及富营养化污染.
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