The 2673sq m site, near Bendemeer Bay, about halfway along the eastern side of the lake, has been owned by the same family for almost 80 years.
It boasts an expansive 54.4m frontage to the Lake Hayes walking track and impressive lake and mountain views.
Its rateable value is $5m.
Colliers agent Brendan Quill, who listed the property alongside colleague Vera Stewart, described it as "one of the best unbuilt sites on a lake in the world".
After bidding opened at $4m, 45 bids were placed before two bidders slugged it out at the end.
Mr Quill said the undisclosed buyer was a New Zealander, but he did not know what their plans were.
Situated in the lower-density suburban residential zone, there is provision to subdivide the section into sites as small as 300sq m.
