Swan and her cygnest swim in diamonds

We looked after Tomos today and after dropping off Dylan to his pre-school, we headed for a walk in Roath Park in glorious warm sunshine. The swan with her eight cygnest that I blipped last week were there swimming on the bejewelled lake. 
Later on we came across a couple of swans that appeared to gracefully and repeatedly rotate in synchrony (extra) as if trying to stir up the water. I don’t think I’ve ever seen this behavour before.