Haven't seen this topic discussed ...
It is common in and around urban areas to see shopping trolleys, bicycles, car tyres and other human "rubbish" dumped into a river. This offends our sensibilities and we want to remove it to make our river look cared for. Often in these same situations, there may be insufficient in-stream or low-level cover.
A case in point: on a recent riverbank clear-up, a Derbys CC wildlife ranger and I carefully took a 20 foot length of corrugated plastic out of the branches of a tree (where it had been left by the winter floods): it was trailing in the river. Once we got it onto land we saw it was covered in caseless caddis. Dilemma! If we throw it on the skip we kill thousands of invertebrates and deny our fishes their feast; if we leave it it looks a mess. We chose to put it back, but we will have another look at the next clear-up in Jul/Aug and re-assess.
My thesis: in these situations shopping trolleys and other "rubbish" can provide essential in-stream cover: they will provide shelter from floods, and cover against aerial predators. Unless we plan to replace the shopping trolleys with equivalent in-stream cover, we should leave well alone, and perhaps even install signs which say something like: "This shopping trolley intentionally left in the river" to indicate that someone is caring for the river.
Please discuss
Andrew
PS Plainly fridges, car batteries and so on should be removed.