I could really use some advice on rivers. I've been trying to fix the Potomac River in Washington, DC, and failed at three attempts so far.

FWIW, I've got several different things going on in there right now to see what renders correctly next week.

natural:coastline seems to be the cheapest, but a total cop out for rivers.

The linked, proposed method descriped in the map features wiki just doesn't seem to work at all.