Considering that the list would include Sharknado, this might not be the worst shark movie of all time - but it's a good contender. Written and directed by the same person (never a good sign), this film lacks in almost every measurable way. The plot is thin - teenagers get trapped on a raft by a shark. That's it. The acting is dire - the opening scene is a master class of how not to seem drunk. The special effects are indeed special - and make Sharknados look expert.
The characters are thin and insist if making unbelievably dumb decisions. My favourite is the short sighted guy who puts his spectacles inside his wet suit - because that's SUCH a great idea. A close second is the idiot who tries swimming while carrying a gun.
It takes itself with a seriousness that only makes it worse. Don't waste your time.