Gridded sea surface hydrographic data along two Salish Sea passenger ferry routes, 2001-2025

Since 2001, several passenger ferries connecting Vancouver Island and mainland British Columbia, Canada have collected sea surface hydrographic data within the Salish Sea. Originally part of two separate monitoring projects in the early 2000s and now maintained by Ocean Networks Canada (ONC), archived and real-time data from these vessels are open to the public. To date, several vessels with scientific underway systems have collected data between Tsawwassen-Nanaimo (TWS-NNO, ∼70 km) and Tsawwassen-Swartz Bay (TWS-SWB, ∼44 km), sometimes up to 8 times per day. This data article describes how the original time-series were obtained, the performance of additional quality assessment, and the steps for creating curated datasets consisting of spatially binned (0.01°) transits of surface ocean water properties in the Salish Sea between 2001-2025. During this period, 30,000+ transits along both routes collected sea surface temperature, practical salinity, and dissolved oxygen; providing dense coverage for a variety of inter-seasonal and inter-annual analyses. Pathways for uncertainty estimation and validation are discussed. Python 3 example code is provided for compiling and processing new data collected after 2025 to enable users to extend this dataset for future analyses.