Identificaciones de fernsibley

Very large fish at TRNWR, between the visitor's center and the seasonal path water viewpoint. At first, I thought it was a nutria, but it slithered in shallow water, never coming up for breath. This one was easily 3-4 feet in length, I saw at least one other that was slightly smaller. "The creature from the refuge." It reminded me of a sturgeon in size.

Could an eagle or heron even attempt something this big?? Seems like it may be rather safe from predation here??