The paper is about monitoring the environment in the Mekong Delta of Vietnam. The delta is an important food supply area in Vietnam, with several environmental issues that may endanger the production. Among the issues are pest insects, saltwater intrusion, floods and water pollution. We are considering Wireless Sensor Networks (WSN) for understanding and controlling risks. A top down design method is investigated that allows geographic deployment, optimization of the layouts, and robust algorithms. This method is based on a simulation technique compatible with the synchronous behavior of the WSNs and future real time interactions.