An equation to predict reaeration rates in natural streams and rivers with wind blowing along the water surface is theoretically developed and experimentally tested. The physical model used in the development of the equation consisted of interfacial layers of water that absorb gas at a rate proportional to an effective diffusion coefficient at the interface, and this surface water is then carried into the main body of liquid by the action of turbulence beneath the water surface. The experimental results give support to the theoretically developed equation. The results indicate that reaeration rates are significantly increased when waves appear on the surface. The increase is often much more than can be accounted for by the increase in surface area. The increase is attributed to the dynamic effect of waves and the wind-induced surface shear stress.