2006) as well as diagnosis of the river health conditions (Plafkin et al. These assessments provided key clues for stream/river conservations (Griffith et al. 1996 Ganasan and Hughes 1998) after regional modifications of the multi-metric model. The health assessment model of index of biological integrity (IBI), based on fish community, was developed by Karr ( 1981) and then applied to numerous waterbodies of North America, Oceania (Harris 1995 Harris and Silveira 1999), Europe (Oberdorff and Hughes 1992 Schmutz et al. The model development and assessments of stream ecosystem health has been one of the hot issues in stream conservation and restorations in worldwide aquatic ecosystems. Overall, our data suggest that land-use pattern and mesohabitat distribution are important factors to be considered for the trophic and tolerance fish compositions and chemical gradients as well as ecological stream health in the watershed. This study remarks the necessity to include additional variables to consider information provided by mesohabitats and land-use distributions within the selected stream stretch. Trophic guilds and tolerance guilds of fish were determined by land-use pattern and these determined the stream health, based on the Index of Biological Integrity. All the habitat patterns were largely determined by the land-use patterns in the watershed. The intermediate fish species in tolerance and omnivorous fish species in the food linkage dominated the community in the watershed, and the sensitive and insectivorous fishes decreased rapidly with a degradation of the water quality. Also, the riffle-reach had high proportions of sensitive fish and insectivore fish, and the pool-reach had high proportions of tolerant species in the community composition. The riffle-reach had a predominance of insectivores, while the pool-reach has a predominance of omnivores. The riffle-reach had good chemical conditions, but the pool-reach had nutrient enrichments. The mesoscale components altered chemical water quality such as nutrients (TN, TP) and BOD and these, then, determined the primary productions, based on the sestonic chlorophyll-a. The mesohabitat structures of pool, riffle, and run reaches influenced the ecological stream health along with some close relations on the fish trophic and tolerance guilds. The objective of this study was to analyze influences on the mesohabitat structures of pool, riffle, and run reaches on the fish guilds and biological integrity in Geum-River Watershed. Previous studies on the biological integrity on habitat and landuse patterns demonstrated ecological stream health in the view of regional or macrohabitat scale, thus ignored the mesoscale habitat patterns of pool, riffle, and runs in the stream health analysis.
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