Working with very large reservoirs

The Western USA is noted for several of its very large water reservoirs, such as Lake Mead, Lake Powell, and what I’m currently working on: Flaming Gorge Reservoir.

Because of the sheer size of this body of water, I’m thinking that I perhaps should be using the tag “natural=coastline” instead of treating it like I would a much smaller lake or smallish reservoir, but I’m trying to decide what tags I ought to be using here to accurately depict this body. Normally, I would use landuse=reservoir (as it is a man-made structure).

I did try to experiment with mapping this reservoir like you would with a riverbank (as it is quite long) with multiple adjacent polygons, but I’ve been running into problems with ways that are very close to 2000 nodes in size… and I’d like to cut that down as I finish up plotting the size of this reservoir and make it in smaller chunks. Altogether, I anticipate this reservoir to have as many as 10,000 nodes on the scale that I’m drawing out the shoreline (where I’m trying to trace the high water line when the reservoir is full). In addition, trying to do the multiple adjacent polygons (besides some weird rendering problems) requires some arbitrary locations to close off the polygon.

BTW, there are some larger islands in this reservoir as well, so there is some added complexity here on top of the usual tags.

Any suggestions on what tags I ought to be using?