@stux we were always taught to walk 30m upstream to check for dead sheep before drinking from a burn. In that distance the corpse water is well enough diluted.

It might not have been 30 metres but it doesn't really matter because what I always did was walk upstream a bit and drink water there which missed the point, looking back.

But with chlorine I expect if the corpse was at the other end of a 25m pool you'd be fine and if i knew they'd drowned in the last couple of hours - as opposed to dying of cholera a week ago, - in the slow lane I'd probably be fine with finishing my laps in the middle lane. Just as long as I know they're not going to drift into my path