Stream temperature plays an important role in closing the energy balance at local, regional and global scales, and exerts significant impacts on aquatic biodiversity, power plant operation and energy production. It is therefore a critical component for representing the energy-water nexus in earth system models. This study is a first attempt to develop a physically based stream temperature model within the Community Earth System Model (CESM) framework. The Model for Scale Adaptive River Transport (MOSART) has been developed to represent riverine water dynamics and incorporated into CESM by coupling with CLM. Here we build upon CLM-MOSART to represent the riverine transport of heat along with water flux and the energy exchanges with the atmosphere. The boundary conditions, i.e., lateral inputs to the stream temperature model are dominated by the temperature of surface runoff and baseflow which is parameterized as a function of soil temperature simulated by CLM. The exchange of energy between river and atmosphere is explicitly parameterized in terms of river water storage, air temperature, incoming radiation etc. Preliminary results with the model applied to the contiguous U.S. at 1/8th degree resolution show that the model is capturing reasonable well the spatiotemporal variability of stream temperature under natural conditions. Moreover, the critical strategies to incorporate the effects of reservoir and power plant operation in near future are discussed.