Ice is water in its frozen, solid form. Ice often forms on lakes, rivers and the ocean in cold weather. Water will freeze at 32 degrees Fahrenheit. Once it gets close to its freezing point, water molecules begin to expand. The expanded molecules make ice a lot lighter than liquid water, which is why ice floats. An iceberg that weighs several tons can still float easily in the ocean, just like a piece of ice floats easily in your cup of water or soda.

Source: National Geographic