The Redwyne Straits is the body of water that lies between the Arbor and the mainland Reach. One must cross the straits to get from Oldtown to the Arbor. Towns such as Vinetown, Starfish Harbor and Ryamsport sit alongside it.
A Feast for Crows
The Redwyne Straits are filled with ironborn warships preying on defenseless trade vessels since the Redwyne fleet is at Dragonstone. After capturing a Tyroshi merchantmen in the straits, some ironborn tried to sneak into Oldtown but were stopped by the Lady of the Tower.