Llyn Goddionduon is a remote lake in the Gwydir Forest in north Wales.

It is totally surrounded by coniferous forest, although a track leads up to it, enabling a water supply in the event of fire, and anglers also use this path.

Some sources state that the correct name of the lake should be Llyn y Goeden (Lake of the Tree), but that an error on the maps resulted in the name Goddinduon (duon means "black" in Welsh, but Goddion is not a known word).

The lake is stocked with brown trout by the Betws-y-coed Anglers Club.

In 1890 an advert for Cobden's Hotel in Capel Curig (over a mile away) stated that this lake could be used by residents for fishing, and the Army Training Camp at Capel Curig still use the lake as a water supply.