Can someone help me find a short story?

$0 - B


Hi, I'm looking for a short story, wondered if anyone might recognise it?

I reckon I read it late 90s, 97, 98 or thereabouts, so not sure how old the story would be. I was about 10 or so, so it could have been a kids one, but I'm really not sure! Whatever it was, it's stuck in my mind and I'd love to find it again. My mum's always had a huge collectiuon of Asimov and Wells, and I remember reading some of it as a kid, so that's a possibility, but I've described it to her and she didn't recognise it.
The parts I can remember are that a town is under a dome of some sort to protect it from the outisde world which is either dangerous, radioactive or something similar. Can't remember the cause, but the dome is supposed to be on earth. Cause might have been war, but I seem to think it was an accident. Main character is a boy who eventually wonders why the river running under the dome contains fish which are unharmed if the outside is dangerous and swims through. (Think he fished in the river, but might have made that up!) He climbs some steps when outside and pushes a lever which tells him the dome is an exhibit in an alien museum. He can see into the dome. From inside I think it looks black outside the dome. I remember there being something distinct about the way the lever gives the description, either it was a voice inside his head, or the voice was described as ethereal, or something unique about it. Irritatingly, I just can't remember what! If I remember rightly, others have already done so and been replaced with robot versions of themselves, and the boy is actually the last human. I vaguely remember his friend trying to dissuade him from swimming.

Any ideas? It's a strange little story and I'd love to find it and read it again now.

Cheers. :D