An endorheic basin , also called an internal drainage system , is a drainage basin , or watershed , that does not flow to one of the Earth 's major oceans . Normally , water that has accrued in a drainage basin eventually flows out through rivers or streams on Earth 's surface or by underground diffusion through permeable rock , ultimately ending up in the oceans . However , in an endorheic basin , rain ( or other precipitation ) that falls within it does not flow out but may only leave the drainage system by evaporation and seepage .