I just got on this forum a couple days ago and love it already!!! Very informative. Thermocline is the biggest drop in temperature throughout the water column. Say your in 120ft of water. If its 65 degrees on the surface and 62 degrees down 75' then all of a sudden it drops to 55 degrees at 80ft. Then 49 degrees at 90 ft, that's your thermocline. Generally salmonoids like it around 49 degrees. And then the rainbows are generally higher in the water column at 55 degrees.