This study quantifies the influence of debris cages on critical submergence at vertical intakes in reservoir configurations. Four model debris cages were constructed of light panel material. A vertical intake protruding one pipe diameter above the floor of a model reservoir was tested in six configurations: open intake pipe, a debris grate placed directly over the intake pipe, and debris cages representing widths of 1.5*d and 2*d and heights of 1.5*c and 2*c, where d is diameter of the intake and c is height of intake above reservoir floor. A selection of top grating configurations and a submerged raft configuration were also tested for comparison. Testing of the model debris cages indicates that the roof or top grate of a debris cage dominates the influence a debris cage has on the reduction of critical submergence of air-core vortices. The side grates of a debris cage have some influence on the formation of vortices. The spacing of bars in the top grate has an influence on air-core vortex development. The presence of a debris cage at vertical intakes in still-water reservoirs reduces the critical submergence required to avoid air-core vortices and completely eliminates the air-core vortex for cases where the water surface elevation remains above the top grate of the debris cage. The potential exists for designing debris cages to fulfill a secondary function of air-core vortex suppression.