Sydridalur is a rather broad valley in the Westfjords close to the inlet of Bolungarvik, wherefrom that village derives its name (vik=creek).
The mountain Ernir separates the Sydridalur valley from another valley,Tungudalur, both close to the inlet. At the mouth of the valley is the sand area Bolungarvikursandur.
There is a fine birdlife in the valley, including bar tailed godwits, eiders, black-headed gulls and meadow pippits.