The first time I had ever seen this, i videoed the entire event as well from entry to exit. It was as if this species swims all the time. I sent it to a frogmouth expert and she had never seen that before. The bird chose to swim and flew away very easily after its swim. There appeared to be no explanation for the bird swimming as it was not particularly hot or anything unusual.
in the absence of a trunk or stone to lean on, a capybara may be an option;
I have observed these two individuals do this twice;
see also
https://www.inaturalist.org/journal/nelson_wisnik/21258-the-friendly-capybara