Trout (/steelhead) that have been conditioned to react to the approach of a line will react to it. I've seen steelhead stacked in a pool that were completely aware of even the most naturally drifting line once ten people thrashed the pool with sloppy casts.
However I've also seen fish in other pools sometimes on the same river that smashed the fly even before a very sloppy mend was completed, meaning the fly was jerked forward and the line making a large crescent shaped tear on the surface.
If fish are holding and many people have been teaching them to beware of that fat string, they will heed that sign. If they have just barrelled in with a fresh tide from a 1500 mile journey to the Aleutian Islands, they might rip into that fly no matter how badly the line looks.
For spooky fish a long leader and floating line is less intrusive than a sinking line unless that sinking line can be presented almost straight down at the fish, in other words without crossing (lining) them in which case deeper or faster currents or fish holding tight to the soft water on the bottom can be better dealt with using a sinking line.
Adapt and conquer, the fish do!
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