I called the DHHS covide hotline today for confirmation and they said surfing and swimming are definitely fine, but there is no detail specifically describing whether windsurfing/kitesurfing is included. The person (a team leader) said windsurfing would be fine though subject to the 5 km limit, etc. I mentioned the Paddle Victoria facebook update, which has a reference to formal notification from DHHS -
vic.paddle.org.au/coronavirus-covid-19-status/ (from the 07/10/20) but they couldn't access that. The Paddle Vic facebook update says "Paddle Victoria has been advised by COVID Directions (COVID-19 Public Health Division, Department of Health and Human Services) that
paddling has been approved within the scope of exercise for Stage 4 Restrictions (advised on 7 September 2020, Transcript ID# 158 123)". It would be nice to have a copy of that transcript!