Unidentified nocturnal bird in creek after dark

It was well after all the birds had gone to sleep but before it was completely dark outside when I was walking home from the service station and walking across the Douglas Street bridge. I looked down at the creek but couldn't make out any details of anything on the ground near the creek. I sort of saw the creek's water which was pitch black in colour. Moments later in the area I was looking at a bird startled and it took off like a rocket under the bridge. It made no sound except for the noise it's wings made on the water as it flapped. It was approximately the size of a duck going on an approximate wing span comparison of ducks being startled on the water in that area.

When this bird took off it did not fly at all and it was about 5 feet into the water from the water's edge. It was retreating like it was pretending it couldn't fly but could still flap it's wings and ran through the water whilst flapping them. It flapped it's wings frantically to move itself across the water to safety. It may have actually ran across the water's surface whilst flapping it's wings. The bird was by itself as far as I could tell. I have, only on rare ocassions in the past, seen this bird night time behaviour before. Only now am I trying to identify the species.

When an Australian Wood Duck is startled during the day they tend to fly away. They can either fly a short or long distance away when startled and have been known to fly at night when disturbed. I do know that sometimes ducks can be heard during the night time but never so early as to just after going to sleep for the night. As this bird was alone I doubt it was a Wood Duck.

I very much doubt it was the White-faced Heron female either as I have yet to hear her during the night time. She is always up early in the morning. As far as I know White-faced Herons are not nocturnal.

Ruling out Australian Wood Ducks and the White-faced Heron leaves only Masked Lapwings and Pacific Black Ducks. It was not a Masked Lapwing as they were all up on Francis Street at the time. This time of the year all the Masked Lapwings flock together as they are not breeding right now.

The Pacific Black Duck is not, as far as I know, nocturnal but I am not ruling it out as a suspect. The Pacific Black Duck rarely makes a sound during the day but I have yet to study this species. It is possible that this bird I saw tonight - well heard flapping across the water - could be a Pacific Black Duck, and what I saw it do is normal startled night time behaviour for this species.

I very much doubt it was an owl or a Tawny Frogmouth as I've never heard of any of them actually feeding in the water. I can also rule out raptors too for this exact same reason plus I don't know of any raptors that are nocturnal.

There are no other known species that spends a lot of time in the water here in Tenterfield that are on my list of what this bird could be. This brings me back to it possibly being a Pacific Black Duck, and possibly nesting somewhere nearby in the water maybe even under the bridge itself. The "possibly" bit is looking more like a "more than likely it was a Pacific Black Duck" than anything else right now. Tomorrow I'll go to the bridge to see if there are any Pacific Black Ducks in the immediate area.