Dee, Welsh Dyfrdwy, river, c.70 mi (110 km) long, rising in the Cambrian Mts., Gwynedd, NW Wales, and flowing NE through Llyn Tegid (Bala Lake), then meandering through a picturesque course NE, N, and NW along the border with England and past Chester to the Irish Sea. At low tide the long, broad, shallow estuary is an expanse of sand, across which the narrow stream flows. Thomas Telford's aqueduct crosses the Dee near Trevor. Sluices at the outlet of Llyn Tegid control the river's flow.
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