Longitudinal profiles of surface water chemistry were made using a Sea-Bird SUNA optical nitrate sensor and a YSI EXO2 water quality sonde. Water from 0.1 m depth was pumped to sensors configured with flow cells from a moving boat, and data were georeferenced with a Garmin GPS and compiled on a Campbell Sci datalogger. Details on the method can be found in Crawford et al. 2015 and Downing et al. 2016. Data were collected between July 10 and Aug 26, 2019 as part of an ecosystem experiment. Two longitudinal transects were made each day. In the morning, the boat traveled southward from the Sacramento Locks to Navigation Light 70. The afternoon transects proceeded while traveling northward. Each point has also been linearly referenced as distance to the northern terminus of the channel. Linear referencing was done in the R programming language after snapping points to a line running through the channel center.