1959 horror/sci-fi movie "classic"
Attack of the Giant Leeches was one of a spate of "creature features" produced during the 1950s in response to cold war fears; a character in the film speculates that the leeches have been mutated to giant size by atomic radiation from nearby Cape Canaveral.
In the Florida Everglades, a pair of larger-than-human, intelligent leeches live in an underwater cave. They begin dragging locals down to their cave, where they slowly feed on them, draining their victims of blood. Two of the first victims of the leeches are local vixen Liz Walker (Vickers), who has been cheating on her husband (Bruno VeSota), and Liz's latest paramour. Game warden Steve Benton (Clark) sets out to investigate their disappearance. Aided by his girlfriend, Nan Grayson (Sheppard), and her father, Doc Grayson, Benton discovers the leeches' underwater cavern. The creatures are destroyed when Steve, Doc and several state troopers blow up their underwater cavern using dynamite.
Text from wikipedia