話說每年美國國慶，亞利桑那州(Arizona)的維多利亞湖(Lake Victoria Arizona)，都會聚集由四方八面而來的青年人，前來開派對尋開心。當中，索女們紛紛著比堅尼上陣，性感到暈；猛男更被攪到慶烚烚，氣氛High爆燈。但他們的舉動，卻惹得本土原住民的討厭。正當成班年青人要盤算，如何應付這群麻煩老坑之際，真正的危機才悄悄出現。深海之下地殼變動，竟然將住在海床200呎之下，絕跡超過2百萬年的原始魔種 食人(魚倉) (Piranha)，全數釋放而出。它們身型細小，神出鬼沒。任何人流出一滴鮮血，成群魔種就會空群撲出，將人喪咬再分屍。恐懼、尖叫、瘋狂血腥，2萬名年青男女完全任由宰割，無處可逃，維多利亞湖亦頓時化作人間煉獄…電影配以頂尖3D特技，將食人魚倉化身成獨一無二的魔種，驚嚇呈現。一場絕望殺戮隨即展開，究竟有誰能夠僥倖逃出生天！？

When flesh-eating piranhas are accidently released into a summer resort's rivers, the guests become their next meal.

A scuba diving instructor, her biochemist boyfriend, and her police chief ex-husband try to link a series of bizarre deaths to a mutant strain of piranha fish whose lair is a sunken freighter ship off a Caribbean island resort.