Identificaciones de ronigreer

Arrived on our dam about 2-3 days ago. Was observed out of the water on the dam bank twice, each time scurrying back into the water, behaviour that we thought was very unusual. Then this morning found deceased on dam bank. No signs of injury. We are assuming a natural death, or perhaps illness.
Also on the dam another HH Grebe (has been there nearly two weeks), a couple of Aust grebes have visited recently, there are daily/nightly visits of Wood Duck (at least 2, often more), plus our domestic ducks.