I think 200 feet is around where you reach the guaranteed death line. Though it's still survivable if you do it right.
Going headfirst should probably kill you pretty fast from 150 ft, but it's hard to guarantee you'll actually be able to do that. But any fall from that high should be enough to kill you, at least from drowning or bleeding out or somegnjng. I'd recommend drinking beforehand, maybe even with some benzos. Hopefully it'd dull you out and assuming the water will be cold, speed up heat loss and induce hypothermia faster.