I hope that eventually someone will perform a much-needed import of water features from a suitable US or state-level data source (such as TIGER or, in my case, MassGIS).

For my personal OSM data based projects, I usually add the MassGIS 1:25,000 Hydrography line and polygon data sets, which are fairly good and could probably be used as basis for an import of Massachusetts water features.

For now, lacking the patience of waiting, I traced all lakes and reservoirs in Wompatuck State Park (Massachusetts, US) from the Yahoo imagery.

On a side note, this was my first time using multipolygon relations in OSM (for the islands). They seem to work fine in JOSM.