The nonlinear interactions of waves with a double-peaked power spectrum have been studied in shallow water. The starting point is the prototypical equation for nonlinear unidirectional waves in shallow water,i.e. The Korteweg de Vries equation. By means of a multiple-scale technique two defocusing coupled Nonlinear Schr(o)dinger equations are derived. It is found analytically that plane wave solutions of such a system are unstable for small perturbations, showing that the existence of a new energy exchange mechanism which can influence the behavior of ocean waves in shallow water.