Bainahumaa barzakhul laa yabghiyaan

بَيْنَهُمَا بَرْزَخٌ لَّا يَبْغِيَانِ

Word By Word:

Bainahumaa  : Between both of them

barzakhul: (is) a barrier

la: not

 yabghiyaan: they transgress

Translation:

Between them is a Barrier which they do not transgress:

Ayah Tafseer:

Between them is a barrier which none of them can transgress meaning, HE has placed a barrier of land between these two types of waters, so that they do not transgress upon each other, which would spoil the characteristics they were created with.

Source: Yusuf Ali Translations and Ibn Kathir Tafseer