it's the very place is where vince viafore and angelika graswald set out on their fateful kayaking tripince went out on this river -- >> yes. >> reporter: they, they launched straight from here to go straight across. you can see bannerman's island and the castle right there across. we've come here with todd wright, a professional guide and outdoor instructor. he's recognized as one of the top kayak safety experts in the world. working with us as a consultant, he's in the same make and model kayak as the one vince owned. how quickly, after falling into water that cold, do you become incapacitated? >> there's that initial cold response and there's panic, your heart rate increases. >> reporter: you're basically hyperventilating. >> yeah, you're hyperventilating. being able to tread water or swim with any kind of efficacy becomes very, very difficult. >> reporter: back on shore, a close examination of the kayak shows something detectives may not at first have realized. that critical drain plug, effectively the alleged murder weapon, is not on the bottom of the kayak. it's on top! now this i