Thanks for your replies. I think the water quality would have a lot to do with the muddy taste and I also think that 'geosmin' in the water is probably responsible. Of course, only by testing the water would it be possible to know for definate.
I've been cooking fish (including trout) for over 30 years and have come across this before but only in trout from stillwaters. I am going to try fishing a couple of different stillwaters to see if the trout taste any better. As I've already mentioned, I'm not especially fond of trout for the table, but, I feel strongly that after paying a substantial amount of money for the privelege of taking a few fish for the pot, they should at the very least be palatable.
John, I'd love to try Avon Springs sometime but it's a fair way to travel for a days fishing. Lakedown is nearer so I'll probably try there next

BTW, whereabouts are you in So'ton? I used to live nr Romsey.