Attack of the Giant Leeches (1959) on Netflix

After local-moonshine swilling trapper Lem Sawyer sees a giant creature, people start disappearing. While searching for illegal traps Steve Benton and Nan Greyson, his girl-friend find Lem dying with giant sucker wounds on his body. One couple Liz Walker and Cal Moulton, forced into the water by her enraged husband Dave Walker, gets taken by the leeches. When police refuse to believe Dave's story, he hangs himself. Soon after this, 2 more trappers disappear, the local Game Warden Steve Benton gets involved. He and Nan's father Dr Greyson realize that the people were taken by the leeches and the leeches live in caves under the swamp. Using dynamite, the 4 missing bodies are discovered and the leeches are destroyed.