There is some amount of agreement that the Great Lakes are to be modeled as natural=coastline. You can see here that natural=water was added and removed just a few months ago:

changeset/27063265

The relations also need some work. For instance, Isle Royale is missing:

way/146305732

Probably along with the many smaller islands in the area there.

I expect the natural=water on the Lake Superior relation is what is breaking the rendering at z13:

osm.org/#map=13/48.0690/-88.5923

I think if you want natural=water to be the standard you should probably open a discussion on the talk mailing list, or someone will just come along and flip it back.

The relation for the forest itself seems to be missing. I got here via this untagged way: way/321248658 which looks like it is meant to be a big piece of the boundary.

Hi-

If you make sure that paths that connect share a node, software that interprets the data will generally work better.

For example, I expect that this way:

way/306192374

Joins up with both Stickney Hill Road and the longer path to the east. Software generally won't make that assumption, it relies on a node being shared by the paths/roads.

I guess data consumers are not widely using it, but it looks like you might also want to make use of the seasonal tag:

seasonal=*

That's all,

Max