This dataset contains results from the monitoring of nutrients and turbidity in three rivers in the Manell watershed in southern Guam, which drain to the Achang Reef Flat Marine Preserve. The dataset contains a series of data tables and a data dictionary for the monitoring that occurred between December 2016 and December 2018. The dataset includes tables on nutrient monitoring, suspended sediment concentration (SSC), results from automated monitoring of stream levels, rainfall and turbidity, and a table of water quality measurements.