Robotic sensor networks (RSNs) find increasing use in environmental monitoring as they can collect data from obscure, hard-to-reach places over long periods of time. This work reports progress in building a network of small, lightweight robotic rafts that will be used to monitor common carp tagged with radio transmitters across Minnesota lakes. We describe the design and architecture of the robotic raft and demonstrate the robustness of our waypoint navigation algorithm through field tests conducted in various lakes. We also present results from experiments aimed at localizing tagged fish. © 2010 Wiley Periodicals, Inc.