Downward propagating internal waves are observed in laboratory experiments. They appear to be generated by the 'obstacle effect' beneath a turbulent surface layer in a surface stress driven stratified flow experiment in a rectangular cavity. The obstacles are the perturbations at the base of the surface layer and the shear is created by a combination of an internal seiche and the circulation in the upper layer. The proportion of energy lost from the surface layer is comparable to increases in potential energy due to vertical entrainment. Consequently, if conditions are favorable, a reduction in vertical entrainment may occur.