The blue duck is endemic to New Zealand where it is found almost exclusively on forested mountain rivers.
Most blue ducks are now confined to forested fast-flowing rivers with scattered rocks and boulders.
They may also been seen on alpine tarns and lakes or even farm ponds, but are unlikely to reside there.
Estimating the population of blue duck is extremely difficult given the often inaccessible habitat in which it lives.
Population estimates of 2,000 to 3,000 individuals have been quoted, but this is likely to be too high. The breeding population in 2003 was estimated to be approximately 500 pairs.