It rises in Cwm Dwyfor at the head of Cwm Pennant, gathers to itself numerous streams which drain the surrounding mountains from Mynydd Graig Goch in the west to Moel Hebog in the east, then flows southwest towards Dolbenmaen and out of the Snowdonia National Park.

Its mouth has been diverted eastwards by almost one mile by a shingle spit resulting from longshore drift.

The Dwyfach itself rises in an area of flat ground to the west of the A487 road between Bryncir and Llanllyfni and flows in a generally southerly direction.

[6] The grave of David Lloyd George, prime minister from 1916-1922, stands beside the Dwyfor in Llanystumdwy.

[7] A boulder marks the grave; there is no inscription; however a monument designed by the architect Sir Clough Williams-Ellis was subsequently erected around the grave,[8] bearing an englyn (strict-metre stanza) engraved on slate in his memory composed by his nephew Dr W. R. P. George.