It is difficult to find details on the Holdfast Bay web site and what I found is different in these two links. The area they recommend as suitable is completely unsuitable.
http://www.holdfast.sa.gov.au/site/page.cfm?u=1022Wind surfers are allowed to launch or retrieve from the Seacliff boat ramp only. They can enter the red areas marked on the vessel exclusion zones map, but must not beach their vessel at any time.
Kite surfers are banned along the foreshore of the City of Holdfast Bay in the interest of public safety and liability.
www.holdfast.sa.gov.au/site/page.cfm?u=1220&c=2890Link showing map of kite surfing area