The hypothesis postulated in this work, looks for to understand the no-linear interaction when a wave travels over a seagrass canopy, and to explain that the presence of a Kelvin-Helmholtz vortex induces to energy transfer in the wave energy spectrum. This energy transfer process demonstrate that the formulations (functions of Reynolds or Keulegan-Carpenter number) for drag force form applied by the seagrass meadow on the wave medium, under-estimate its value; additionally, this vortex can released long waves without the need of a wave breaking process.