"Ocean".

"Ocean phobia" is commonly referred to as "Thalassophobia." It's an intense and irrational fear of deep waters and oceans. This phobia can encompass fears of venturing into deep waters, encountering marine creatures, or not being able to see what might be beneath the water's surface. Symptoms can manifest as anxiety and distress even when thinking about or viewing deep waters, and it may impact a person's ability to engage in maritime activities or have ocean-related experiences in general.