I foiled from Point Walter to the Old Swan Brewery last summer. It does get a bit sketchy once you get past Pelican Point. I did toy with sailing further into the city. The wind wasn't super strong but constant enough to stay on the foil.
After looking at river charts on the Transport WA web site I am glad I didn't. Not much water depths except for the dredged channels. Here is the chart:
www.transport.wa.gov.au/imarine/coastaldata/nauticalcharts/pdfs/WA898_swan_and_canning_rivers.pdfIn the middle of the Perth Water (body of water between CBD and Como) the depth is charted between 0 and .7 meters depending on tide.
It gets deeper again past Heirsson Island and I have seen what looked a foible section of river around Burswood were the race track is. The wind seems to funnel into that area in certain Easterly directions. Not sure what the water quality is up that way and how many bull sharks are lurking.