We analyzed fish community dynamics in fishways in the Yeongsan, Nakdong, and Geum river watersheds in South Korea and evaluated fish passage efficiency using a multimetric fishway assessment model, along with analyses of water chemistry and flow regime, from April to October 2016. The dominant fish in the fishways was Erythroculter erythropterus, with a mean relative abundance of 28.5% in all three watersheds. Omnivorous species and tolerant species were the dominant fish guilds in the fishway communities. The highest frequency of fish passage through the fishways occurred during the spawning season from April to June. During the summer monsoon, flow velocity increased rapidly and juvenile and young fish rarely passed through the fishways, which demonstrates that fish passage decreased significantly with increased current velocity (R² = 0.463, P<0.05). The ecological health, based on the fish health model, and the trophic state, based on the nutrient regime, were evaluated in the three watersheds. Overall, the multimetric model of fish passage efficiency, based on structural, hydrological, and biological metrics, showed that the Yeongsan fishway was the most suitable while the other two fishways were unsuitable.