Interesting! I've seen them on the middle of that string of three dams previously, but only in small numbers and that was a couple of years ago. The late season occurrence is also interesting. Nice record.
This dam had very little water in it when I visited on 20 October 2019, and I wouldn't be surprised if it had dried up completely long before any rains came to refill it. It always makes me wonder if/how they survive in situ or whether they have to re-populate from elsewhere. So many questions, so little time...