The Redwyne Straits separate the Arbor from the mainland of Westeros. They are controlled by House Redwyne of the Arbor and House Hightower of Oldtown, who both have ships patrolling the waters. The area overall is under the authority of House Tyrell of Highgarden.
In the books
In the A Song of Ice and Fire novels, the Redwyne Straits are usually peaceful. They are a center of trade, with ships passing through the straits from the city of Oldtown and ports on the Arbor to all parts of Westeros and Essos, as well as the Summer Islands and Stepstones. In ancient times the straits were less safe, with the ironborn sometimes raiding as far south as their waters.
Towns such as Vinetown, Starfish Harbor and Ryamsport sit alongside it.
Old Oak · Red Lake · Goldengrove · Bitterbridge · Tumbleton · Grassy Vale · Cider Hall · Ashford · Horn Hill · Brightwater Keep · Bandallon · Honeyholt · Oldtown (The Citadel · The Hightower · Starry Sept) · Uplands · Blackcrown · Three Towers · Sun House · The Arbor