While playing with my GIS software, I discovered that the USGS had released 1/9-arcsecond NED data for my county. This data is generated from LIDAR scans and has a resolution of about 1/3 meter in x/y/z.

After much trimming and fiddling to reduce the data size, I created 0.25m contour lines and picked those that looked "best" for the water body outlines. I then used the same GIS software to simplify the lines, reducing some of them from over 1000 points to less than 200 but still maintaining nice curves. I the used Ian Dees' shp2osm package (java, not the perl stuff in svn) to convert to .osm, and used josm to create relations for the islands and some other cleanup.

It was quite a bit of work; now that I have a better handle on the process I'll have to try it in other areas to see if it's useful for "production" mapping. But it was a worthwhile exercise. (I should try to come up with some before/after images to upload).