I have to admit, I really do not understand water temps that much. I know some general things, but I'm not knowledgeable enough to figure out the nuances of why it matters if the water temperature is 42° or 46°, etc.. It seems that it must be important as much attention as posters seem to pay to it, but I just don't get it. If you know within 10 degrees or so, don't you probably have enough info?