海

1. Origins, structure, and basic meaning

• Structure: 海 (うみ) is a noun for the ocean or sea and, by extension, a seaside setting for activity.
• Basic usage: 青い海が見える makes the visible body of water the subject, while 海で泳ぐ marks the place where a family swims.

2. Common pitfalls and similar expressions

• Visible body of water and activity setting
  • In 海が見える, が marks what comes into view, while in 海で, で marks the activity location. The second should not be recast as swimming in a pool near the sea.