not sure of the depth the exact depth, but i am sure you can put a boat that size on thurston, no problem. its been six or more years ago, but my dad and i used to put a 16' lund on there all the time.
i was out there just this past weekend (with no luck) but the water seemed high enough to launch something that size. in my opinion, that would be preferable to a smaller boat or canoe the winds down there are vicious and can pick up in an instant. i don't know about you, but i wouldn't want to be battling that in a canoe.