Why not google for the line you remember? That gives you Alasdair Clayre's verses immediately:

THAMES LIGHTERMEN.

At Waterloo we passed the trains arriving from the west
The old stockbrokers piling out all hot and neatly dressed,
We passed their banks and offices and we saw them crowd inside,
And there we lay and watched the sky, and drifted with the tide.

And as we shot through London Bridge, with half an inch to spare
The people up ahead of us leaned across the ledge to stare
Their office doors were shutting and their cash was changing hands,
And we stripped off our shirts, to bask,like kids on Margate Sands.

One lovely summers morning, as we left Brentford Pier
The wind was blowing south south-west and the air was warm and clear,
Five swans were drifting down the tide like white clouds in the sky,
And the oil and muck were breaking white in spray where we passed by.

But I've seen the river running clear, before the diesels came
I used to pole a punt at night and play the courting game
By Brentford Reach you'd dip your mug to drink when you were dry
You could see a swans's feet trailing wide to turn and let you by.

But the men who rowed the barges once are old and going grey
The rivers turned to oil and muck, and we've watched the job decay,
And aching bones and worn-out spines are all the thanks we've got
One day they'll dam the whole Thames up and let the lighters rot.

a song by Alisdair Clayre, about the demise of the Thames bargee's and their way of life.