Agricultural land use degrades water quality and reduces wildlife habitat, but drainage water management (DWM) may alleviate those impacts. With DWM, farm fields are seasonally flooded to create wildlife habitat and to retain nutrients. DWM successfully creates habitat for migratory ducks, but its effects on water quality have not yet been examined in the Pacific Northwest or in similar climates. We examined DWM in a corn-pasture farm in western Washington state, USA. The farm has sub-surface tile drains, which are open and draining during the growing season and blocked after fall harvest, creating a temporary wetland. The goal of this pilot study was to understand nutrient release during the growing season, when fields are drained. Later, we will assess nutrient release during flooding. We measured nitrogen (N) and phosphorus (P) concentrations in the ditch and in the tile drains prior to and during the growing season. The tile drains were a source of nutrients, with higher N and P concentrations than in the ditch, but the receiving ditch was effective at removing nutrients: N and P concentrations were lower downstream than upstream. Prior to planting, the ditch removed 0.3 mg N/L and 0.02 mg P/L along its 400 m length. After planting and fertilizer addition, the ditch removed 0.04 mg N/L and 0.03 mg P/L. The ditch drained slowly, with discharge always <25 L/sec, and the bottom substrate was almost entirely fine benthic organic matter. The combination of slow flows and organic-rich sediments may have enhanced its ability to remove N and P and we expect that slower flows in winter will further reduce nutrient export.