The goal of this project, funded by NOAA’s Coral Reef Conservation Program and requested by local partners, was to monitor water quality in three rivers that drain to the Achang Reef Flat Marine Preserve at the southern tip of Guam, in order to provide a baseline of conditions for environmental managers. The spatial and temporal variation of turbidity, suspended sediment concentration (SSC), and nutrients were determined at sites on the Ajayan, As Liyog, and Sumay rivers. Using Guam EPA water quality standards, SSC and turbidity in the rivers were generally classified as excellent to good, although occasionally the waters were ranked as fair, particularly on the As Liyog River during higher rainfall. Overall, nitrate was found to be in the excellent range, and orthophosphate generally in the good to fair range. There was some evidence that a number of the parameters showed decreasing trends in concentration during the project. Further monitoring would help determine if these decreases are real, which could be an indication of the benefits of the ongoing restoration activities in the watershed, evidence of natural revegetation subsequent to wildfires, or a combination of both. In any case, additional restoration efforts along with public education and outreach would be helpful to further reduce runoff to the rivers that drain to the Achang Reef Flat Marine Preserve.