Background and Purpose: Narrow-leaved ash (Fraxinus angustifolia Vahl) is one of the most important tree species of lowland floodplain forests in the Republic of Croatia. Recent significant climate changes, reflected in extreme temperatures and long dry periods, have had a direct impact on the dynamics and levels of groundwater, as well as on the dynamics of precipitation and floodwater, which are of decisive importance for the success of narrow-leaved ash. Our study aims to determine the morphological and physiological characteristics of seedlings of narrow-leaved ash after 72 days of drought, normal watering and substrate saturation. Materials and Methods: The experiment was established in three treatments (drought, normal watering and saturation), and each treatment included two containers or 24 seedlings. A total of 72 seedlings were replanted. After 72 days, height growth and increment, water potential, photosynthetic efficiency and the total chlorophyll content in the leaf mesophyll were measured. Results: Seedlings from the drought treatment wilted immediately. Seedlings saturated with water up to the root collar manifested better height and diameter growth, high water potential and a lesser physiological stress response as compared to the seedlings that were watered normally. Conclusions: Seedlings of narrow-leaved ash, which is a hygrophytic tree species, do not tolerate dry conditions and no watering. Seedlings saturated with water for 72 days showed a better morphological-physiological status than the seedlings that received normal quantities of water.