Any vibrating structure submerged in fluid experiences the opposing force of the fluid opposing vibration. The effect of the fluid on structural dynamics is known as “added mass”. Runners of hydroelectric turbine generators are subjected to various excitation mechanisms. The natural frequencies and mode shapes of a runner are important parameters which determine its behavior and response to these various excitations. Added mass effect lowers natural frequencies of a system while submerged in water as compared to in air. This paper outlines the concept of added mass and compares the natural frequencies of a runner in air versus water as calculated via Finite Element Analysis (FEA). The FEA model was initially validated through experimental modal analysis (EMA) performed on the runner removed from the turbine generator. FEA and EMA results are compared and discussed.