As I've overdosed at Mallory Park recently and the rivers here were STILL too coloured, on Monday, I had a session on the Grand Union Canal. The sun also put in an appearance for the first time(well when I've been off work) in absolutely ages, well it sure seems that way.
I'd not fished there for at least a month which is very unusual for me in summer, so it was nice to be back.
I arrived at about 10am, finding the water relatively coloured but a few small roach topping in the broken sunlight. The fish didn't respond how I expected though, turning away from my usual killing patterns but looking. A change to slightly flashier pattern changed that but the bigger rudd I expected to find, with the sun out, were nowhere to be seen.
I walked much further than I usually would, finding plenty to cast to but nothing bigger than hand sized.
A roach to a glass bead(clear) PT, size #20.

A couple of boats went through, which does disturb the fish but not for very long here when the sun is out. After it had settled for ten minutes I started to find plenty of small rudd...

Then had this small bream/rudd hybrid to a silver ribbed blk and peacock spider, #16.

This was a new species (sub species) on fly for me, although years ago I regularly had them of about 3lb apeice to bait. They are no longer present in that area though or I'd be trying for them everyday...a 3lber looks totally stunning.
Getting bored of the rudd I moved to an area up from where the river joins the canal, this was stuffed with little chub. I hoped some would move into the canal above the locks as there are very few upstream, in the canal proper.

Here I took the above roach/micro chub combo.
By 1:30pm I'd caught about 40 fish (roach, rudd, little chub and the hybrid) but had had enough so started a brisk walk back keeping an eye out for a better fish. Eventually I spotted a couple of rudd of about half a pound apeice in the middle of the canal, sunning themselves. I got into possition and was stripping some line off my reel ready to cast when to my right I noticed 8 or 9 way bigger ones on the far side. "Forget the half pounders!", I thought and moved my possition to cover the "proper" ones, which were lying at the side of a willow next to the far bank reeds. I'd never found the big rudd in that area before although they are always somewhere in the mile long pound.

I took four over a pound in the next ten minutes, all to the silver ribbed B+P spider. This one of at least 1lb 8oz being the best.

and in the net...

Was a good session even without the bonus big fish to end on, but they made it extra good...stopped me whining about the rivers for a bit.
Dee

Once again good result sb Dave, my local river is in awful condition, it is high coloured and stinks. Visibility varies from 8 inches to a foot or so, the floods round here have been bad.
Tried a stilwater last week , never had a touch, the colour of it was pea green, again zero visibility. The tiny patterns I was using soon disappeared out of sight, tried some bigger flies still nothing.
In your experience what level of water visibility would you decide not to fly fish and call it a day?

That really depends on the venue, if it is stuffed full of fish and the time of year is right then I'll happily fish with near on zero visibility but not on just any water. As a rule the harder the venue the more you need water clarity, so if the matchmen all catch 100lb a time, don't worry if it is coloured but if they struggle for a few fish then forget it, unless it is very clear and you can see fish.(or they are rising like mad...rare on hard venues but given the right conditions)
The carp/coarse lakes I fish typically have only a couple of inches to a foot of visibility. I can catch from all of them "blind" but some work better than others, this year I've struggled on the match lake but last year that was one of the easiest venues.(change in temp., as last year was so hot?)
In winter when some of the colour drops out(carp not grubbing about in the slit so much) then the silver fish fishing can improve but again not on all waters. Some venues can be a total waste of time when it gets a bit chilly.
It's all your own experimenting, as there won't be a load of local flyfishers to ask, unlike if you were to go to a trout reservoir, but work at it and you'll end up with a network of venues that you will know well enough to be abled to catch from all year round.
Dee

Thanks sb Dave, it certainly seems the case were some waters produce fish to the fly, were as otheirs do not. Weird