Dataset refers to the study where we measured rates of spectral wave dissipation across a dense and extense (over 1 km long) seagrass meadow comprised of Posidonia australis in southwestern Australia. It includes high-resolution flow measurements within and above the seagrass canopy. These observations were used to quantify the effectiveness of three different approaches to predict observed rates of spectral wave dissipation. The results show that the canopy flow velocities induced by short period wind waves were less attenuated than longer period swell, explaining the frequency dependency of rates of wave dissipation, with shorter period waves being more efficiently dissipated by the meadow.