Williston is not a lake you want to be on if you have no experience on the lake, big water or boating in general.
It is a lake full of logs, deadheads, sandbars and fluctuating water levels. It blows like an SOB here and when it blows, the lake gets crazy, ocean crazy.
McKenzie is a dying town and trying to find a boat rental will be tough. I don't remember any back when we used to visit the town.
But the fishing is amazing!! And the scenery is second to none! The north west side of the lake or the Peace reach are both great places to visit
You can try this place
http://www.williston-lake.com/?page=summer-activities
Cheers
SS