The Trident is a river in Game of Thrones. It is one of the largest and most well-known waterways on the continent of Westeros. Technically it is three rivers which flow into one another just before they reach the Narrow Sea, several hundred miles north of King's Landing.
The three main rivers of the Trident - the Green, Blue and Red Forks - and their numerous smaller tributaries give the Riverlands their name.
In the books
Location of the River Trident (in red) on the continent of Westeros.
The Red, Blue and Green Forks of the Trident, show in the appropriate colors. The main body of the river is colored orange.
The River Trident is the most extensive river network on the continent of Westeros. It flows out of the hills and low mountains of the eastern Westerlands and the bogs of the Neck into the Narrow Sea. It consists of three major branches.
The Red Fork
The longest branch rises in the Westerlands and flows north to the confluence with the Tumblestone. The Tully castle of Riverrun is located where the two rivers meet. The Red Fork then flows east through the very heart of the Riverlands to where it joins the main body of the Trident. For much of its length the Red Fork is meandering and slow-moving, with frequent sandbars and islets. There are fords a few miles south of Riverrun and another ford, known as the Mummer's Ford, further east.
The Blue Fork
The shortest and least noteworthy of the three branches rises in the hills south-east of Seagard and Ironman's Bay. It flows south-easterly into the main body of the Trident.
The Green Fork
The Green Fork starts in the bogs of the Neck, technically within the southern borders of the North, allegedly close to the location of the mysterious Greywater Watch, the seat of House Reed. The river flows south, crossing the border into the Riverlands, and then past the two towers of the castle known as the Twins, the seat of House Frey. It flows south-east for several hundred more miles before reaching the main body of the Trident. Just before that confluence is the Ruby Ford, where the Battle of the Trident during Robert's Rebellion was fought and where Robert Baratheon slew Rhaegar Targaryen in combat.