In order to answer questions that involve multiple and potentially interacting hydrological flowpaths, multiple tracers with identical transport properties that can nonetheless be distinguished from each other are required. We are therefore developing such a new kind of engineered tracer system that allows a large number of individual tracers to be simultaneously distinguished from one another. This new tracer is composed of polylactic acid (PLA) microspheres into which short strands of synthetic DNA and paramagnetic iron oxide nanoparticles are incorporated. The synthetic DNA serves as the “label” or “tag” in our tracers that allow us to distinguish one tracer from another and paramagnetic iron oxide nanoparticles are included in the tracer to facilitate magnetic concentration of the tracers in water samples. The potential advantages of this strategy compared to conventional tracers are the elimination of background interferences, the ability to segregate superimposed flowpaths through the design of strictly unique DNA tags and the biodegradability of the tracers.