Where two seas meet... but do not mix!
These two bodies of water were merging in the middle of The Gulf of Alaska and there was a foam developing only at their junction. It is a result of the melting glaciers being composed of fresh water and the ocean has a higher percentage of salt causing the two bodies of water to have different densities and therefore makes it more difficult to mix.
This occurrence is explained by Allah in the Quran:
And it is He Who has let free the two seas (kinds of water): this is palatable and sweet, and that is salt and bitter; and He has set a barrier and a complete partition between them.
(Al-Quran, surah Al-Furqan, Chapter 25, Verse 53)
Masha Allah. Subhanallah