Indigo Lake
... that Indigo Lake in Ohio's Cuyahoga Valley National Park is not a natural lake?
... that <b id="mwAmY"><a href="./Indigo_Lake_(Ohio)" id="mwAmc" rel="mw:WikiLink" title="Indigo Lake (Ohio)">Indigo Lake</a></b> in Ohio's <a href="./Cuyahoga_Valley_National_Park" id="mwAmg" rel="mw:WikiLink" title="Cuyahoga Valley National Park">Cuyahoga Valley National Park</a> is not a natural lake?