The effects of renovation measures for improving the hypolimnetic anoxic condition in Lake Nakaumi were simulated using the two existing models. The first simulation experiment was carried out with the following premises: 1) a 200-m cut in the Moriyama and Omisaki dikes to the bottom, 2) construction of a tide dike in the place of Nakaura tide gate and 3) filling up of the deep holes created by dredging in the eastern side of the lake to the bottom level. The simulation data were used in 1992. The second simulation experiment was conducted by changing only the second of the above three premises, i.e., instead of construction of a tide dike, the existing Nakaura tide gate was used, while the remaining two premises were kept similar as in the first case. The simulation data were used in 1998. The third simulation was conducted with another change in the second premise, i.e., the Nakaura tide gate was opened for navigation. All the simulation results showed effective improvements in the hypolimnetic condition in the western part of the lake where the anoxic condition disappeared throughout the year. However, the anoxic condition still persisted in the eastern part of the lake in these simulation studies.