I caught a limit in about 90 minutes right below the Raybob release before Christmas. Water was boiling all around but there was about a 15' section where it was relatively still or had a little eddy. Every time I threw in there I got bit quick.
So my thought is that's an extreme case, but I look for a spot with slack water if the creek or river is moving much. I'm not a great crappie fisherman, but that's one data point for you anyway.
I knew that You are a gracious and compassionate God, slow to anger and abundant in lovingkindness, and one who relents concerning calamity.