Ferns beside a still pool

Mammals

Native and introduced species along Murray River

In terms of regular sightings, various mammals are the next most commonly seen animal along the river. Grey Kangaroos and Swamp Wallabies being the most common. I've listed a number of the species that I saw below.

Platypus and Echidnas Monotremata

An old branch of mammals that lay eggs rather than giving birth to live young!

Platypus Ornithorhynchidae

Platypus
Platypus (Ornithorhynchus anatinus) were occasionally seen in the pools within the alpine national parks. Many reported seeing these all the way down to the Hume Dam

Echidnas Tachyglossidae

Small mammal covered with coarse hair and spines
This Short-beaked Echidna (Tachyglossus aculeatus) greated me as I started my journey from Bringenbrong Bridge.

Marsupials Marsupialia

Most of the Australian native mammals are included in this large infraclass with the exception of a few notable examples like bats, rodents and marine animals. Since most of the Australian mammals are nocturnal, many would be about while I was recouping from the days paddle in a deep sleep. Because of this I only really saw the ones that like to stay up late early.

Eastern Grey Kangaroo
Eastern Grey (Macropus giganteus)Macropodidae
The most commonly seen animal along the river.
Swamp Wallaby
Swamp Wallaby (Wallabia bicolor)Macropodidae
While hard to spot sometimes, these little guys would often stay still by the waters edge as you floated by.
Koala
Koala (Phascolarctos cinereus)Phascolarctidae
Rarely seen from the river, but this thirsty guy came down to drink on a very hot Australian summer day.
Common Wombat
Common Wombat (Vombatus ursinus)Vombatidae
Common above Lake Hume, but I wasn't lucky enough to see one in person.

Modern Mammals Placentalia

Most of the animals from this group that you will likely see are going to be introduced farm or feral animals. Australia does have some placental mammals such as native bats and rodents along with around 50 marine species such as seals, whales, dolphins and dugongs.

Dingo fits into a fuzzy area, it is definitely a recently introduced animal but it also has fulfilled a role that larger extinct carnivorous marsupials once played for many thousands of years now and helps regulate other feral populations like foxes.

Large rodent swimming
Rakali (Hydromys chrysogaster) is a large native aquatic rodent with a distinctive tipped white. Also known as the Australian Water Rat.
New Zealand Fur Seal
New Zealand Fur Seals (Arctocephalus forsteri) were seen sunbathing and playing around the barrages.
Dingo on rock
Dingo (Canis lupus dingo) sizing me up after I interrupted his pack hunt of a Sambar Deer.

Common Feral Animals

Pig
Pigs (Sus scrofa) are a fairly common feral pest in the basin, especially around the more arid sections.
Herd of a dozen goats on the river bank
Most goats (Capra hircus) seen are likely to be farmed on the Murray River, but some feral goats will be present in areas.
Horse
Horses (Equus caballus) is one of the more destructive animals in the alpine areas, especially when population numbers are not controlled.
Sambar Deer
Sambar deer (Cervus unicolor) were commonly seen around the alpine areas.
Fallow Deer
Fallow Deer (Dama dama) were a smaller and shyer species, but I startled a number of these (and myself) while hiking around Kosciuszko National Park.
Red Deer
Red Deer (Cervus elaphus) are one of the least commonly seen but the largest deer species found, mostly limited to the alpine areas.
Red Fox
Red Foxes (Vulpes vulpes) was commonly seen along the river.
A lot of cows in the river
Feral cattle (Bos taurus) is unheard of, but farmed animals can still have a fairly negative impact on the river system if they are allowed to roam freely into the river.