You can see them. No predators=no fear of anything. A tip though, the big ones are smart, so if you cast towards the lily pads a little further out, you may have a chance at something closer to 6-7". For their size they sure do fight hard. What I like, is that no rules that apply to another fish seem to apply to them. On a hot day you can wade out and literally drop the bait on your foot,and they will take it. Usually fish spook at a bobber dropping heavily on the water, they are indiferent. If you want to know how close they can be to shore:
This is shore
This is a fish. Distance to scale. When you aproach they will head deeper. Most are in about 3' of water, but like I said earlier, the big ones hide out under the lilypads in deep water. I have never done this, but if you have a new fly to test, that would be a good place to start. The only two things I dislike about them are that sometimes, you will see two big fish aproach the bait, they will start to fight over it, and a smaller fish will come and snatch it. They are also expert at stealing bait. You can combat this by using extra small hooks, and hooking the bait firmly. They do not seem to care about presentation, so you don't really even need to leave an end hanging. Oh, and by the way, they hate powerbait.