Churyeong Stream flows 37km from the mouth of Lake Okjeong and is impeded by many weirs that hamper the active movement of land-locked sweet smelt fish (Plecoglossus altivelis) that ascend and descend between the lake and the upper stream. In late December 2006, a fishway was constructed in a weir of the lower reach of Churyeong Stream, where juveniles begin their ascent to mature upstream. At 13 sites along the stream from April to October 2007, we investigated the effects of the newly constructed fishway on sweet smelt growth. After construction of the fishway, juvenile sweet smelt were able to migrate freely upstream, something that had previously only been possible when the weir was in flood. The body size of mature sweet smelt collected during the spawning season in September 2007 was greatly increased compared to previous seasons, measuring an average of $163{pm}21.5mm$ in standard length. These measurements were 13mm, 20mm, and 57mm longer than body length averages for mature sweet smelt collected in 2006, 2004, and 2005, respectively. Therefore, it is likely to be necessary for the construction of fishways on streams and rivers containing land-locked sweet smelt populations to increase average body sizes and viability.