i lived in Canberra for three years - the lake was occasionally closed for swimming due to blooms, but many of us sailed regardless. i took my cues from the true locals who seemed not to worry so neither did i, and we were all fine. <-note, this is
not medical advice!
Burley-Griffen is top sailing on a summer's evening easterly - after work I'd join the sailors clustered at the point, rigged and waiting for the tell tale swing to kick, then bam! sail 'till dark. great summer sailing.
the winter fronts in ACT are fickle and the water feels only just above freeze point. i tried a sail once in June, fell in and as soon as my head went under, i had instant ice-cream headache. limped back to shore and never did it again.
back on topic - the man behind the ACT windsurfing forum was Jase, who I think moved to the coast not long after I left in 2010. he still posts here forum a lot, so he may be able to advise...