In general, more and larger fish are found in more productive waters. Makes sense; more productive water can sustain a higher amount and diversity of forage, which is great for fish production. So what do you look for?
A good start is to find zones where the steeper, higher elevation sections of river transition into lower gradient, meandering channels. As the water slows down and warms slightly in these areas, it is capable of supporting a higher diversity of invertebrate species that trout prey on. These areas also generally create better holding water for large fish. Undercuts on the outsides of meanders, large woody debris from the riparian area, and deep, slow moving holes are all hangouts for the big boys.
However, a slower moving river alone isn't necessarily enough to create a more productive environment. Nutrient enrichment which fertilizes water can create a boom in productivity. This is generally characteristic of more downstream reaches, after agricultural inputs and water treatment facilities have added nutrients such as nitrogen and phosphorous to the water. Too much of this is a bad thing, as it causes the water to become anoxic, but the right amount can do wonders for a water. For this reason, it is often a good idea to target waters that pass through agricultural areas.
There are certain things to look for that can be tell tale signs that a water is productive and capable or producing some beastly fish. Periphyton, or moss growing up from the substrate (though it can be a PAIN when fishing) is an obvious indicator of good primary production. Primary production supports bugs, which supports small fish, which support big fish! Another thing to watch for is the presence of small bait fish darting around as you wade. Similarly, crayfish are a great sign that big fish can be present.
So! Point is, it may be harder, but you don't need a ton of time, or far off destination to catch large, even trophy fish. Get out and explore, find your local waters that fit the description for a hog farm, and work it over, persistently. It's worth it!