This article describes the design methodology for a network of robotic Lagrangian floating sensors designed to perform real-time monitoring of water flow, environmental parameters, and bathymetry of shallow water environments (bays, estuarine, and riverine environments). Unlike previous Lagrangian sensors which passively monitor water velocity, the sensors described in this article can actively control their trajectory on the surface of the water and are capable of inter-sensor communication. The addition of these functionalities enables Lagrangian sensing in obstacle-encumbered environments, such as rivers. The Ishikawa cause and effect design framework is used to ensure that the final system synthesizes the diverse operational and functional needs of multiple end-user groups to arrive at a broadly applicable system design. A summary of potential applications for the system is given including completed projects performed on behalf of the Department of Homeland Security, Office of Naval Research, and the California Bay-Delta Authority.