You're in luck Mandurah has some excellent spots. Both ocean waves, bump and jump and estuary flat water blasting. This time of year there's not that many waves, we need a 2m swell for it to get interesting.
There's 2 great speed spots, but you need a good weedy, the flat water is caused by weed cutting out the chop. Coodunup bay (Fangys) or Kiter's beach Wananup (liptons).