Photosynthesis and transpiration were measured for a stand of the emergent plant, Zizania latifolia (Gasses.) TURCZ. at a sheltered shore of the Hitachi-Tone River, Japan. Net photosynthetic rate per unit leaf area at light saturation was 12 μ mol CO₂⋅m^-2⋅s^-1, which is in the lower range for emergent plants. The daily course of net photosynthesis and transpiration had no midday depression, i. e. the maximum was recorded around noon. Vapor pressure difference did not regulate leaf conductance at photosynthetic photon flux densities saturating net photosynthesis.