The goal of an Active Localization algorithm is to choose measurement locations to minimize the uncertainty of the location of a target as quickly as possible. This research is motivated by deploying mobile robots to find radio transmitters, for which we are developing novel algorithms and systems. Currently, we are working with researchers at the University of Minnesota who are interested in studying the movements of invasive fish in nearby lakes. A general method for localizing low-power radio transmitters has a wide range of applications such as defense, search and rescue, environmental monitoring, or wildlife tracking.