Synonyms for the phrase "heavy sea" include rough sea, stormy sea, choppy sea, raging sea, and tumultuous sea. These are terms used to describe the condition of the sea that is characterized by strong waves and winds. Heavy seas are common in areas with harsh weather patterns and can cause danger to vessels and swimmers. When the sea is rough, navigation becomes difficult, and boats are at an increased risk of capsizing. In contrast, when the sea is calm, it poses no additional risk to navigation. Understanding the synonyms for "heavy sea" can help individuals plan for safe and effective navigation when out on the water.