I don't think there are Aqau Natal classes as such, however I did Aqua Aerobics all they way until 38 weeks pregnant! You can do them at the Hayya Club in the Meadows Centre or at the Le Meridien Mina Seyahi.
Clink on the link for the Facebook page of the Aqua Aerobics Classes at the Meadows, which should have all the info you need!
http://www.facebook.com/pages/JAquaCise-Aquafit/155137677825