Hiked in June. It was rather wet but that was no problem. The falls are gorgeous and definitely worth the ascent. Walking along the lake is beautiful, too. The RAC Karri Valley Resort allows walk-ups (i.e. those who are not staying there overnight) for canoe/kayak rental by the hour. We wished we had budgeted time for this into our day.
August walk. Was a bit soggy and a part is a huge puddle but with an easy bypass. It looks like the winter has been very hectic and there are a lot a branches and trees across the track. However they are easy to navigate around.
River is running fast and the falls are in full glory.