Being an old novice a "hot swim" to me can be caused by a multitude of reasons no more so than its just the right habitate for the fish being caught in it, ie: feeding, water flow, bottom contour, weed etc etc. the time of day will affect a hot swim also wheather conditions. I would think that the amount of times a hot swim is fished will affect it as well. When I look at a venue to fish, river or lake? I allways look at the bank first then check out the water if the bank is well used which could indicate a hot swim, but could also mean an overfished swim.
I usually move on to look for a quieter spot still checking out the water and the bank as I go until I see what I am looking for I then stop and look at the swim itself. If fishing close in I want cover, if fishing at lenght then I want a little more space to cast, you can usually find what you would call a hot swim without casting a line into the water. To sum up a hot swim is somewhere you find where you feel confident in finding the fish you are looking for and one that you think is where the fish will be. You learn the art of finding the "Hot Swims" with your experience of fishing unless like me your still looking.
Happy hunting