Water temperature is the most important thing I go by, but if you track it year after year, you will see trends on the lakes you fish and you can predict it based on the calendar. For me here in the southeast counties, small lakes might start fishing well in more of a shallow spawning/prespawn pattern as soon as you get a string of stable warm spring days in April that starts pushing water temps up... and then when it hits 60 around early May they are spawning big time. It usually winds down around Memorial Day with mostly males guarding nests by that point, but we've caught big females with eggs well into June.