It's a lake/marsh/wetlands, somewhere in Japan.
Not:
Lake Hyoko, near Suibara town, Niigata region known as the Swan Lake But very good! You got all the catagories, so I'll count that as a legitimate guess and won't deduct a question!

Not
Kabukuri Marsh
Not Lake Shikotsu
Biwa-ko Lake, Japan
5 questions to go.
Don't forget to give the "region" Try what Island!