Treated wastewater-supported rivers are common throughout the world. In arid and semi-arid environments, treated effluent is often the only source of perennial flow in these systems. Effluent discharge can create and maintain aquatic habitat, but there are challenges, including microplastic pollution. Microplastics are ubiquitous worldwide and include primary microplastics, like microbeads, and secondary microplastics, such as fragments, film, and fibers. Although modern wastewater treatment plants remove the vast majority, microplastics are still present in treated effluent.