An in situ system has been developed for the detection and localization of groundwater inflows into shallow estuaries and tidal rivers. The system is largely composed of commercial, off the shelf (COTS) components and is portable so that it can be adapted for use on a variety of platforms. The basis of the approach is the use of a multiparameter sensor suite that can be assembled to exploit differences in the chemical, biological and water quality composition of ground water and estuarine water. The associated data acquisition system maps the bathymetry and distribution of N water characteristics. Real-time displays are selectable for time series display, display of "clustering" of water characteristics in water characteristics space and event marking. High-resolution navigation displays allow precise revisiting of potential inflow sites detected in the current or previous surveys. We describe the system, the acquisition and post-survey processing software and how the system is employed. Results from recent estuarine surveys are presented. The system is intended to be easily and inexpensively reproduced by other potential users. A system description and generic data acquisition and post-survey processing software will be available through the Cooperative Institute for Estuarine Environmental Technology (CICEET).