Lake Kabetogama (Minnesota)
I don't think that there is a lake beginning with Q; so-- Lake Rukwa.
If I may backtrack for just a minute, to fill in the missing "Q":
Quebec River
(category is bodies of water, including lakes and rivers)
Upper Delaware River (scenic and recreational river)
or Utah's Salt Lake
Lake Wobegon!!
No. no, try Windermere
Lake Xau, Botswana (courtesy of MSN encarta)