The region drained by the Tweed River consists mostly of the caldera of a huge, ancient, extinct volcano. The branches of the river join at Murwillumbah and flow about 20 kilometers north-east to Tweed Heads where they enter the sea.
The Tweed River area has a fine subtropical climate, high rainfall and fertile volcanic soils. It was originally covered by rainforest, much of which has been cleared. Some remains in several national parks and reserves. The lowlands along the river are used for farming sugar cane and other crops.
After receiving the Gala on the left, the Tweed crosses the north-western corner of Roxburghshire past Melrose and, after being joined by the Leader on the left, winds past Dryburgh Abbey round the south-western corner of Berwickshire.
(1600) the Tweed uplands were the favourite hunting ground of the Scots monarchs, and, at a later date, the Covenanters found refuge in the recesses of the hills and on the banks of Talla Water, an early right-hand affluent.