Source: The Great Interpretation of Dreams (Ibn Sirin)
A calm, clear sea in a dream indicates a just king, goodness, and prosperity. Swimming in it indicates entering the king's service and gaining benefit.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
A calm sea indicates a stable life and abundant sustenance. For the traveler, it is safety, and for the sick, it is recovery.
Source: Signs in the Science of Expressions (Ibn Shaheen)
A calm sea is interpreted as a just king. Whoever sees himself drinking from it will gain money from the king.