Is it normal that i'm scared of deep water?

When I was a young child, my brother used to tell me that there were 'giant man-eating catfish' at the bottom of the local lake my family and I go to for vacation. The fear of the tell-tale 'giant man-eating catfishes' still haunts me even though I know that catfish aren't at the beach area we usually swim at. I also have a problem where I hallucinate my fear or something close to my fear when in deep water (I am a pessimist so this may be a link to the hallucinations).
I cannot swim alone because of this. And by this I dont mean the catfish thing alone, I mean huge rocks, seaweed, houses (there are tales that houses are at the bottom of the lake), boats (these too), cars (these too), dead bodies (from drowned victims), and many more things. I just hallucinate or imagine being yanked down into the water with no escape.