Explorer Allan Cunningham crossed the river at Gravesend in 1827 and named it after his patron, Lord Gwydir, who took his title from Gwydir Castle in Wales.
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Gwydir was named for the Gwydir River (which in turn was named by the explorer Allan Cunningham after his patron Lord Gwydir, who took his title from Gwydir Castle in Wales).
It is used for the mitigation of water from the Gwydir River upstream, between the Gwydir River, which runs through the village of Yarraman and the Mehi River, downstream which runs through the town of Moree.