Which brought the thought that it would rapidly be colonised by fish and weeds and riverine invertebrates. By the time it was removed, it would be sheltering species, well on its way to becoming its own tiny ecosystem.
I'm not the first person to think such things; meet the Bath Marine Preservation Society's Trolly Reef, and follow on down the comments for the eerily beautiful Original Abandoned Shopping Trolley Project.
All of which leads me to wonder how much of conservation is about returning an area to an idea of appropriate wildness. The plants and animals don't especially care, they will happily grow through concrete, tarmac, old bikes and shopping trolleys. You could argue about rust, broken glass, sharp edges but moss and murk will happily cover all of that, given time. And the wildlife would probably appreciate being left in peace.