Lotus plants grow in the moat of Maizuru Park, Fukuoka City, but the growing area is decreasing year by year in these several years. It is estimated that the causes of the growing area decrease are feeding damage by tortoises and/or the leaf submersion caused by torrential rain from rainy season to summer. In this study, effect of leaf submersion on the subsequent growth of lotus was investigated. One and two months old lotus plants were submerged for 6, 12, 24 and 48 hours in the water in June and August 2012. After the submersion, they were cultivated for four weeks and leaf growth was investigated in every week. Number of leaves died and disappeared water-shedding property increased by the submersion for more than 24 hours. The more the temperature during submersion, the more number of leaves died. The leaves proliferated after submersion showed well-growth when the plants were submerged within 48 hours. From these results, it was thought that the submersion of the leaves was not a direct cause of the decline of the lotus plants in the moat of Maizuru Park, Fukuoka City.福岡県舞鶴公園の濠に生育しているハスが近年衰退しており, その原因としてカメによる食害や梅雨から夏にかけておこる集中豪雨による葉の水没の可能性があげられている. 本研究では, ハスの葉の水没がその後の生育に及ぼす影響について調査した. 2012年6月および8月に1カ月齢および2カ月齢の株への水没処理を行った. 水没処理時間は, 6, 12, 24, 48 時間とし, 水没処理終了後, 4週間栽培を行い, 1週間ごとに葉の枯死・撥水程度を調査した. ハスの葉は24時間以上の水没で枯死葉が増加し, 気温の高い時期ほど, また株齢が進むほど枯死葉, 撥水性消失葉の増加が顕著であることがわかった. しかし, 48時間以内の水没であれば, その後展開した葉が健全に生育を続けたことから, 葉の水没は舞鶴公園濠のハスの衰退の直接的な原因ではないと考えられた.