After my recent struggles in high densitiy altitude at Big Bear Lake, I made a second attempt to kick off my water bodies tour.
I learned that I can use Skydolly’s Location module to essentially start cold and dark anywhere. 
Float plane pilots, look here: Sky Dolly v0.16 - Free Flight Recorder & Replay, Location Management - #57 by Steeler2340
So I made my way up Hudson River, starting just North of NY, to be clear of their class B. I had to divert from the river just a bit near Poughkeepsie, to keep clear of their class D.
I’m using a number of bridges addons, which I found just following the river on the flightsim.to scenery map.
I’m now South of Albany, which I will circumvent also because of, you guessed it, airspace.
