How to identify symbols?

Just installed BaseCamp 4.8.12 to go with my shiny new 66i.  the default TopoActive NA map shows icons: blue circles with a wavy symbol along the coastal areas of Puget Sound.  I cannot find anywhere in BaseCamp what they mean.  Ive used older versions of BC with my 62sc, but these aren't waypoints since they arent selectable.  their maps have no legend and Garmin support sites have little useful information.

thanks,

Glen