Severe water stress is responsible for reducing plant growth and reproduction. This study aimed to evaluate the physiological and biochemical mechanisms associated with the tolerance of two genotipes of bahiagrass (Paspalum notatum Flügge) with different ploidy level to water deficit and flooding at the reproductive stage. Photosynthetic performance of diploid and tetraploid plants was not affected by flooding. In contrast, the water deficit decreased stomatal conductance, increased leaf temperature, and resulted in a decrease in the assimilation rate of the two genotypes. Despite the greater activities of antioxidant enzymes, flooded roots accumulated hydrogen peroxide and malondialdehyde. Roots of plants exposed to water deficit maintained an accumulation of biomass similar to that of control plants; however, with higher levels of total phenol content, total soluble sugars and proline. Diploid plants subjected to flooding had more inflorescences, however, the drought reduced the total number of filled florets per plant. Less starch degradation allows the maintenance and recovery of biomass in the tetraploid genotype, which allows it to maintain its reproductive performance even under drought conditions. Overall, the synthesis of osmoprotectants and activation of antioxidant machinery are important strategies in the tolerance of bahiagrass to water stress at the reproductive stage.