Current methods for screening large numbers of bacterial colonies for phosphatase activity, rely heavily on the use of colorimetric assays. While such methods have been applied extensively in the laboratory, they are not without their drawbacks. We here describe a precipitating fluorescent probe that can be used to screen phosphatase activity in bacterial colonies. This probe can be incorporated directly into agar plates used to culture the organisms of interest. The approach offers several advantages over current methodologies including the ability to monitor the development of phosphatase activity with colony development, and the ability to distinguish between activity arising from cell-bound and cell-free enzyme. This enzyme probe was successfully used to detect and isolate phosphatase-producing bacteria from activated sludge.