In order to properly manage the quality of water in Juam Lake, distributions and growth characteristics of submerged plants in Boknae flood control reservoir were investigated. In addition, the total amount of nutrient load by submerged plants were investigated. The total vegetation area was 1,146,849 m^2 of total flood control reservoirs (1,848,568 m^2) before flooding. By August 19, all of Boknae flood control reservoir was flooded during rainy season. Dominant plants were MISSA (Miscanthus sacchariflorus), SCPMA (Scirpus fluviatilis) and CRXDM (Carex dimorpholepis) which occupied 87% of all flood control reservoirs. The total amounts of organic matter loads at different submerged plants were great in the order of CRXDM (501,642 kg area^-1) > SCPMA (20,987 kg area^-1) > MISSA (3,413 kg area^-1). The total amounts of nitrogen loads by CRXDM, SCPMA and MISSA under different submerged plants were 56%, 3.9% and 0.8%, respectively. The total amounts of phosphorus loads at different submerged plants were on the order of CRXDM (1,842 kg area^-1) > SCPMA (78 kg area^-1) > MISSA (14.8 kg area^-1). Therefore, the results of this study suggest that organic matter, T-N and T-P in water quality of Juam lake were strongly influenced by submerged plants in flood control reservoir.