Whenever I pass a river, preferably with a bridge, I always stop on the bridge, face downstream and say to myself, "Out with the bad," as the current carries it away.
Then I turn and face upstream and say to myself,
"In with the good," as the current rushes toward me.
I stay facing downstream or upstream as long as I need and I remember to breathe deeply.
This is one of my favorite ways to let go of stress, clear my head, and ultimately be filled with a sense of calm. Once my head is calm I'm amazed at the creative ideas, observations about the river and happy thoughts that fill it.
It's simple, and it works for me more often than not!
P.S. Ocean waves and waterfalls also work.