Hydromys chrysogaster, also known as rakali and in times past, water-rat. It’s Australia’s beautiful large aquatic rodent with webbed feet, water-proof fur, white-tipped tail and carnivorous appetite. Studies in Sydney hint that this species is able to defend its territory from introduced vermin i.e. they keep rats and mice at bay and probably predate upon them. Rakali may also live in symbiosis with platypus sharing burrows see: http://www.platypus.asn.au/the_australian_water_rat.html
As a burrowing mammal rakali are considered pests by some irrigators, but paradoxically they may be a major predator of crayfish and yabbies, known abundant dam and dyke burrowers.
I recently managed to shoot this video clip with help from friend Ian with boat on the Murray River in Yorta Yorta country. Rakali is very active so I have slowed the speed 50% start and end of clip for ease of viewing.
For more species from Yorta Yorta country, keep posted.