Pretty much every duck in Victoria can be see at the Western Treatment Plant. The only exception might be the Plumed Whistling Duck, which is not easy to see in Victoria at all.
However, there are two ducks that you have a chance of seeing but are not so easy at all: Freckled Duck and Blue-billed Duck. If you do see them, chances are you’ll see 1-2 individuals, compared to the thousands of Australian Shelducks in the summer. Actually, you have a much better chance of seeing them at Lake Lorne in Geelong, but if you don’t want to make a detour there, here’s something you can try at the Western Treatment Plant.
Go to Lake Borrie via the first entrance on Point Wilson (Gate #5). After going through Gate #6, go in the direction of the red arrow:
As you pass the the head of the arrow, look to the right. For some reason, this smaller inlet seems to be a haven for these rarer ducks. Now you pretty much have to scan every duck with binoculars. Look around quickly because these ducks have a tendency to swim away if they can tell that you’re there. Here is a Blue-billed Duck we saw the last time we were there, and we’ve seen it more than once:
Yes, it’s a male Blue-billed Duck! Keep in mind that the Blue-billed Duck can dive underwater so it pays to look at every area a couple of times. The Blue-billed Duck has an intricate mating display that involves water splashing but we’ve never seen it.
If you can tick the Blue-billed Duck and Freckled Duck, then the other ducks in Victoria should be a piece of cake. After that, one trip to Cairns and the surrounding areas should allow you to see every duck in Australia. (I’m excluding the Northern Mallard here.)