OpenStreetMap
I was under the impression that in the U.S. the USGS' National Hydrography Dataset (NHD) had been loaded into OSM. In some areas it appears to be present, but not in others. For example, at or near the the map location associated with this entry is Gem Lake, but it does not show up in any of the renders.
Discussion
Comment from SK53 on 1 February 2010 at 18:47
NHD data is imported basin or sub-basin. The import areas are chosen by individual mappers according to personal interest. You can see who might be importing areas in Colorado, here for east of the Continental Divide, and here for west of the Continental Divide. Osmarender gives a reasonable overview of whether hydrography has been covered in a region (e.g., for Colorado.
Importing the data is only the first step, each import requires substantial effort to clean-up the data. I think anyone who has looked at Colorado basins is not keen on the idea of doing huge imports over Denver, Colorado Springs and other conurbations, as these may hamper the efforts of other mappers. Even sub-basins are pretty large and likely spill out into densely mapped residential areas. Furthermore if any water features have been mapped then it is an important courtesy incumbent on the importer to preserve any prior manual mapping work.
The French CORINE data import only imported areas where they did not interfere with existing mapping. I think a similar approach has been discussed for NHD data on the us-talk list.
HTH