Low-temperature (typically 5–75°C) fluid, commonly referred to as "diffuse" hydrothermal flow, emanates from fractures over a significant portion of the Juan de Fuca Ridge seafloor in the Northeast Pacific Ocean (Kelley et al., 2012, in this issue). Although some fraction of the diffuse effluent becomes entrained relatively quickly into nearby plumes from high-temperature sources, a number of studies suggest that a significant portion flows laterally as discrete low-level plumes that remain detectable downstream for considerable distances (Trivett and Williams, 1994; Kinoshita et al., 1998, Veirs et al., 2006). The seafloor near diffuse hydrothermal vents supports densely populated, localized biological communities in a bottom boundary layer (BBL) environment that is highly variable in both space and time. Currents, temperature, and turbulence in the BBL, in addition to a complex array of biological, chemical, geological, and other physical factors, influence community structure near diffuse vents. Tides strongly affect the flow direction of both high-temperature (Veirs et al., 2006) and diffuse (Kinoshita et al., 1998) plumes within the water column, and have been observed to affect temperature in the immediate vicinity of diffuse vents (Little et al., 1988; Tivey et al., 2002; Sheirer at al., 2006). Here, we describe recent measurements that reveal in greater detail the important role that tidal advection plays in modulating the BBL environment near diffuse hydrothermal plumes.