Al-Furqan 25:53

Wahuwa allathee maraja albahraynihatha AAathbun furatun wahatha milhunojajun wajaAAala baynahuma barzakhan wahijranmahjoora

And it is He who has released [simultaneously] the two seas [i.e., bodies of water], one fresh and sweet and one salty and bitter, and He placed between them a barrier and prohibiting partition.

He is the One who joined the two seas, so as this is sweet, very sweet, and this is bitter, very bitter, and made between them a buffer and an insurmountable barrier.