This project applies mathematical models to study the effects of organism movement and the structure of stream systems on the survival of species and the spread of waterborne infectious diseases. Stream habitats have a dendritic structure, and organisms in stream environment undergo both random dispersal and water-driven drift. Human activities (e.g. constructing a channel or dam) and severe weather conditions (e.g. flooding and drought) may affect the stream network structure and water flow rate. This project aims to understand how these factors may affect stream populations and waterborne disease outbreaks. The results may contribute to better usage of stream resources, protection of stream species and improved responses to waterborne disease outbreaks. This project will offer research opportunities for both undergraduate and graduate students. The investigator will use graph theory tools to describe the stream network topology and differential equation models to study population dynamics. The research tasks are as follows: (1) finding the optimal distribution of resources and optimal harvesting strategies for single species network models; (2) studying the impact of the connectivity of networks and downstream boundary conditions on the competition between two stream species; (3) investigating the properties of the basic reproduction number and the endemic equilibrium of an epidemic network model; (4) simulating a cholera outbreak. The project activities initiate with