large water offen have names - but they did noch have define borders because they are parts of the coast, a sea or the name waterpart will be diffine by costlines and islands. (example north sea, baltic sea, english channel, …)
one step larger can be found here: http://www.openstreetmap.org/?lat=52.6074&lon=5.0764&zoom=14&layers=M Hoornse Hop is part of the larger lake IJsselmeer. If you scroll around on the map in the area, you will find different similar names e.g. Gooimeer (Southern part) . Is there a fundamental issue where at a certain size this does not work anymore? It is annoying though, that the current renderer only shows the name at a zoom level of 14 of more detailed, for areas like the North Sea that is not sensible.