Fykiaphobia

Fykiaphobia is the fear of and  in open waters. Fykiaphobes can also be afraid of other Aquatic plants (or at least in appearance), such as large arrangements of coral, large beds of algae, and other such slimy growth-like marine life. Fykiaphobes will often refuse to enter open water and dirty ponds.

It is also natural to get unnerved abruptly in a rush while swimming in the beach when your leg touches or get tangled by a seaweed or plastic that can resemble the physical form of the other things in this list.