Abstract:The Naoli River Watershed is one of the important grain production bases in the Sanjiang Plain, northeast China. After over 50 years of agricultural development, this region has not only tremendously contributed to China‘s grain production but has also accumulated great wealth to this region. However, environmental degradation trends in the region have been observed due to overemphasizing the pursuit of economic efficiency and ignoring natural environment protection. This paper assesses the biotic integrity in the Naoli River Watershed using the Index of Biotic Integrity of the Benthic Invertebrates (B-IBI). The aquatic benthic invertebrate data were collected in July 2007 from 21 sample sites both in the main stream and 3 tributaries. After identification of these benthic invertebrates in the laboratory, B-IBI index were calculated using both the three scoring method and the ratio scoring method. Both methods come with identical assessment results. Statistical analysis shows a significant positive correlation between the scores of the stream B-IBI and the assessment results of the water quality as well as the habitat quality. The overall score values of the B-IBI in this region are generally high with only a few individual sample sites scoring poorly. Among the 21 sample sites, 15 of them can be classified as in good condition without or with little human impact, covering 71.4% of the sample sites; 5 as in average condition with medium human impact, covering 23.8% of the sample sites; 1 as in poor condition with severe human impact, covering 4.8% of the sample sites. The study illustrated that the sample sites with high-scores are mostly located either in the tributaries or the upper reaches of the main stream in the mountainous areas, covered by dense forest with little human activities; the sample sites with low-scores are adjacent to human settlements and normally located in either the outlets of the tributaries or the middle reaches of the main stream with low riparian vegetation coverage, poor water quality, intensive human activities, and intensive land use. Therefore, it can be concluded that the land use and land cover (LULC) have had a significant impact on the stream B-IBI of the Naoli River.