Loch Broom is fed by River Broom which rises in the Dirrie mountains. issuing from two lochs, Loch Bhraoin and Loch Droma. Loch Bhraoin feeds the river Abhainn Cuileig which is joined by the Allt Breabaig stream that rises in Sgùrr Breac to the south. Loch Droma feeds the river Abhainn Droma. The two rivers join close to Cuileig Power Station, 4.75 miles southeast of Loch Brown, passing Leal Forrest before joining the loch as a fast flowing river with a strong current. Loch Broom opens from the Minch at a width of 12.5 miles, covers 7 miles south-eastwards, and holds the Summer Isles over that distance, and ramifies into Loch Broom proper in the North, with the sea loch, Loch Kanaird to the northeast close to Isle Martin, which overlooks Annat Bay on the Scoraig peninsula to the west which separates Loch Broom from Little Loch Broom in the middle and Gruinard Bay in the South. At its mouth proper, Loch Broom is 4 miles wide, and travels 5 miles south-eastward; contracts to 1 mile wide and changes direction to south-south-eastward and goes for about 9.5 miles where it is fed by the River Broom.