Subject: Reason for round lake in Quebec

If you look at a map of Quebec, Canada, you will see an almost perfectly round 
lake roughly 35 miles in diameter that has the complete center as an island. It 
is located at 51.40402 N, 68.68403 W on a map. The name given on a map 
is "Riviére Manicouagan". It appears as though the lake is the result of a 
meteor strike, or a volcano, but if this is the case, why is the complete 
center "filled", instead of being a deep hole? How would the center fill in, 
and leave the outer edge deep enough to form a lake?

Re: Reason for round lake in Quebec