The Nooksack River watershed comprises the majority of the Water Resources Inventory Area 1 (WRIA 1) located in Whatcom County in Washington State. From its headwaters in the northwestern Cascade Mountains, the Nooksack River drains approximately 809 square miles, comprising most of western Whatcom County, including agricultural areas and the developed lowlands surrounding the towns of Deming, Everson, Lynden, and Ferndale. The Nooksack River enters the Lummi Indian Reservation at its eastern extent, which contains the majority of the Nooksack River delta before it discharges into the marine waters of Bellingham Bay. The Nooksack River is also the primary source of freshwater into Portage Bay, which is located approximately 5 miles southwest of the Nooksack River delta. Continuous nitrate monitoring data were collected at three sites in the Nooksack Basin. The first site, located on Fishtrap Creek near Lynden, WA (USGS site ID 12212050), is a tributary to the Nooksack River. This site is influenced by nearby farmland/agricultural land runoff making it an important location for monitoring nutrient loads into the main stem of the Nooksack River. Data were collected from April 28, 2018 to December 31, 2021. At a second tributary site, Kamm Creek near Lynden, WA (USGS site ID 12211390), data were collected from October 7, 2019 to December 31, 2021. Lastly, the third site was located at the mouth of the Nooksack River at Ferndale, WA (USGS site ID 12213100) from March 30, 2019 to December 31, 2021. Existing USGS stationgages at the Nooksack at Ferndale and Fishtrap Creek near Lynden allow for the computation of nitrate estimated loads during the monitoring period. The daily nitrate estimated loads data provided in this data release are computed using approved USGS nitrate concentrations and river discharge. There is not a discharge record at Kamm creek, and therefore only approved nitrate concentration data is available via the National Water Information System (NWIS - https://waterdata.usgs.gov/nwis).