Dark, murky water and logs or dark objects in it. I've been fishing for 10 years (since I was 3), and I have this fright. I even love being around water. the water.
Here is an example. I was at a picnic with my family and some friends a while back at a canal. If you walked up past the dam, you would come to an area where it was completely covered in a thick film of algae. Over the algae covered water was a bridge that was partially collapsed and was all rusty. Some of the boards had fallen off too. On the far shore, there were logs turtles sitting on them that looked scary, even though I love all animals. The entire scene was almost indescribable because it looked like something from a movie. It was themost scary area of water I have ever seen and I still have nightmares about it.