Hydrographic variability and dynamics in the Gulf of Maine are examined through the investigation of δ18O_w and salinity properties of coastal surface waters. Data from Gulf of Maine waters sampled over a decade, from 2003 to 2015, including a suite of samples that were collected monthly from April 2014 to March 2015, are presented. These water samples fall on a mixing line between Maine River Water (MRW) and Scotian Shelf Water (SSW). However, slope waters likely also contribute to these surface waters. The seasonal variability in water samples collected during 2014 and 2015 indicates the strong influence of river runoff on coastal Gulf of Maine surface water properties. The coastal surface Gulf of Maine mixing line presented in this paper is a needed baseline for reconstructing hydrographic variability in bicarbonates using oxygen isotopes.