After finding the Rainbow Serpent I went looking for information about what the river was like back in 1825. I believe I might find some images at The State photo collection held in John Oxley Library and photo and cuttings files at the Queensland Historical Society but that will have to wait until I am back on my feet.
I did find some wonderful descriptions of what was found by those first Europeans.
From Dr Ros Kidd's report for the PA Hospital
In 1825 the lower reaches of the Brisbane river were described as a ‘veritable garden of Eden.’1 Dense vine-clad jungles festooned with blue and purple convolvulus adorned both banks

and perfumed salt-water lilies floated on the tidal edges.

Around the site of the future Brisbane primeval forests of gums, bloodwood and ironbark clothed the ridges, and the flats nurtured patches of thick pine and figtree. Fish, reptiles, bird-life and mammals abounded.
And from Archibald Meston, a supposed expert in Aboriginal matters who arrived as a youth in Brisbane in 1870,
The city site was covered by thick scrub, and the botanic gardens area filled with tulip trees or Maginnchin.

South Brisbane was clothed in dense bush fed by several small creeks flowing from nearby swamps. Men crossed the river, fishing from bark canoes made from broad sheets of stringy bark or casting their heart-shaped towrow nets to encircle shoals of mullet. Others used vines to climb the trees for possum and koala which were despatched with stone tomahawks. Women and children dived in lagoons for lily roots, dug yams and collected the edible fern roots. Some sat on the banks weaving their baskets and bags from the pink and green swamp grasses while youngsters frolicked in the shallows.
The primeval forests on both banks of the rivers nurtured staghorns and elkhorns

and fragrant orchids

while bush turkeys foraged in the shadowed scrub. Flocks of parrots raided the blossoms while pelicans fished the sandbanks.

Ducks and swans in their hundreds trawled the waterways.4 Kangaroos abounded on the southern bank later named after them.5
It must also be noted that Brisbane was set up as a penal colony for repeat offenders. It was a harsh brutal place. The triangles were in constant use for beatings from the lash. The convicts hated the gailors and the gailors hated the convicts. It would be diffictult to appreciate beauty under these circimstances. When free settlers did arrive they came for all kinds of reasons. The Irish to escape the famine, the Scottish who were displaced from the Highlands, Germans fleeing religious persecution and others just wanting a better life.
An early painter of Brisbane was Conrad Martens. He had been the artist on board the Beagle Joining the boat in Montevideo in July 1833. Also on board was the British naturalist, Charles Darwin. Martens and Darwin forged a close friendship which would last a lifetime. He painted this watercolour in 1862 sending it as a present to Darwin. He painted this from the street I live in at the spot where all the pythons were living last year.

I have spoken to several elderly people here in Brisbane who can remember when the river was crystal clear.

Now you wouldn't let it touch your skin or clothing and if you do you carry the smell.

Only remenants of the bush, the birds and animals remain. The indigenous people were rounded up and place in "protective custody" 260 Km away. The river was "developed".
In such a short time it was all gone.
1 A convict transported from Redcliffe in 1825, quoted by ‘an old Brisbaneite’ in the Brisbane Courier, 22.3.1930.
4 Meston, A, ‘100 Years - Black Man to White Settlement’, The Daily Mail, 1.12.23.
5 Meston, A, ‘Moreton Bay and Islands’, in Handbook of Excursions, Australasian Association for the Advancement of Science, Pole, Outridge & Co, Brisbane, 1895:20.