Charles Ellicott Commentary Isaiah 23:3

"And on great waters the seed of the Shihor, the harvest of the Nile, was her revenue; and she was the mart of nations." — Isaiah 23:3 (ASV)

By great waters the seed of Sihor ... — Sihor (“the dark river”) is, as in Jeremiah 2:18, a Hebrew name for the Nile.

The grain trade with Egypt (Ezekiel 27:7, which adds the linen trade) was naturally a chief branch of Tyrian commerce. In practice, since the Egyptians had no timber to build ships and, for the most part, hated the sea, their navy consisted of Phoenicians. Tyre effectively reaped the harvest that sprang from the Nile’s inundation.

For “mart,” read gain. The “great waters” are those of the great sea, that is, of the Mediterranean.