Psalms 89:25 - Matthew Poole's English Annotations on the Holy Bible

I will set his hand, i.e. establish his power and dominion. In the sea; the midland sea. The rivers, to wit, Euphrates, called rivers in the plural number, as Nilus also is, Isaiah 18:1 Ezekiel 29:3,4, in regard of divers branches of it, and rivers which flow into it. So here is a description of the uttermost bounds of the Promised Land, Exodus 23:31 Numbers 34:3, to which the Israelitish power was extended by David and Solomon.