MT's tip about line counter reels got me thinking about a better way for me to locate deep water fish like Lakers and Walleye in the summer or at least to get a better sense of optimal trolling depth.  I would like to find some kind of fishing thermometer - a device that I could attach to my line and lower down to take temperature readings at various depths (a digital read out would be best.)  I don't use a depth finder and don't plan to but does anyone know of some kind of small device that would work for my purposes.  I've tried Googling fishing thermometers but haven't found anything that looks very promising.