Ocean vs. Sea vs. River vs. Lake: Key Differences in Size, Salinity, and Flow

Ocean: Vast saltwater bodies covering 71% of Earth (5 oceans); avg depth 3,700 m; max 10,911 m (Challenger Deep).

Sea: Smaller saltwater bodies, often partially enclosed (Mediterranean, Caribbean); avg depth ~1,000 m.

River: Flowing freshwater channel from high to low elevation; empties into ocean/sea/lake; avg depth ~1 m.

Lake: Inland water body (fresh or saline), natural or artificial; surrounded by land; avg depth ~50 m.

Hierarchy: Oceans > Seas > Rivers/Lakes. Salinity: Oceans/Seas high; Rivers/Lakes usually fresh. Flow: Rivers flow; others largely static (tides/currents excepted).