Winter is time to do some homework.

[BobH]

I live and fish in southern New Jersey and most winters its gets cold enough for the lakes to freeze, at least once. Most of the lakes in this area are spring fed. So what does that mean? Well, this spring fed water is warmer than the ice that's covering the lake, take note to were you see slushy or open water areas in the middle of the ice, especially when there is a bit of snow, this is where the underground spring exits into the lake.
During the winter this is the warmest water around, so when the ice melts this may just be one of the places you want to check out, since fish are naturally drawn to the warmer water during this time.
In the summer when water temperatures rise, these springs are still at work pumping out the same temperature water, as in the winter, that might just be a bit more oxygenated than the warmer water in the rest of the lake.
It's allot easy to find this places in the winter than summer unless you keep a thermometer on board to probe the various areas of the lake.