The Blue Fork has its source in pure springs and marshy terrain south of Seagard and the Twins. In order to get around the Blue Fork when it swells its banks, one must travel through Sevenstreams and Hag's Mire.
Harwyn Hoare, King of the Iron Islands, began his conquest of the riverlands by landing one hundred longships south of Seagard and marching them overland to the Blue Fork. His ironborn then used rivers to conquer the riverlands from the Storm King, Arrec Durrandon, with their greatest victory being the battle at Fairmarket.
A Game of Thrones
After departing the Twins, the army of Robb Stark sweeps around the headwaters of the Blue Fork and travels to the Whispering Wood. Robb's host is joined by small lords, hedge knights, and masterless men-at-arms.
A Storm of Swords
Robb's army travels north from Riverrun toward the Twins for the wedding of Lord Edmure Tully to Roslin Frey. The Blue Fork is flooding its banks, however, with rising waters washing out the bridges at Fairmarket and Oldstones. When Galbart Glover and two others try to cross at Ramsford, two horses and one man are drowned and Galbart clings to a rock until being rescued. Robb's host thus rides around the Blue Fork, passing the ruins of Oldstones, rills and brooks near Sevenstreams, and the bogs of Hag's Mire.
A Feast for Crows
All the way up the Blue Fork they rode, past Sevenstreams where the river unraveled into a confusion of rills and brooks, then through Hag's Mire, where glistening green pools waited to swallow the unwary and the soft ground sucked at the hooves of their horses like a hungry babe at its mother's breast.—thoughts of Catelyn Stark