Spring fed rivers with natural reproduction tend to get earlier runs. It's not uncommon to see fish beginning Mid-July in these rivers. As said before day length windows are a major factor in both salmon and steelhead runs (steelhead more so in the spring than fall) that most don't take into consideration. It seems like every year we debate whether there are early runs happening, when in reality runs are very consistent from year to year. Those who study run timings closely know when they should be on the water.