Evaporative losses from small seasonal water reservoirs in semiarid regions may significantly diminish storage and water availability to rural communities. Motivated by finding effective and economically feasible measures for suppressing evaporation, we study the efficacy of self-assembling floating covers in suppressing evaporation under field conditions and potential ecological ramifications of the covers. We conducted a multi-season study with eight identical small reservoirs (13.5 m(2) area and 1.5 m deep) using ethylene-vinyl acetate foam disks (200 mm in diameter, 15 mm thick) in white and black to cover six reservoirs (cover fraction of 91%), leaving two uncovered reservoirs for control. Physical attributes such as evaporative losses, radiative balance, temperature, and heat fluxes were measured and compared with modeling results. Evaporation suppression under field conditions ranged between 65% and 80% in the summer. Despite significant differences in energy partitioning, evaporation from white and black disks were relatively similar (similar to 20% for white and similar to 30% evaporation for black disks compared to uncovered reservoir). Replacing black disks with water filled black polyethylene balls improved suppression efficiency and diminished seasonal variations (similar to 80% suppression irrespective of season). We developed a physically based model to describe and extend the experimental findings by exploring effects of reservoir management regimes on evaporation and to optimize cover and reservoir characteristics for different climatic conditions.