1. In a saucepan, combine chicken broth, onion and celery. Bring to a boil and cook about 2 minutes.
2. While broth is boiling, blend yogurt, lemon juice and dill in a small bowl. Season with salt and pepper and set aside.
3. Season salmon on both sides with salt and pepper. Add to skillet with broth mixture; cover and reduce heat to a simmer. Poach until fish just starts to flake when prodded with a fork, 8 to 10 minutes.
4. Lift salmon out of broth with tongs or a slotted spoon and serve warm with a generous dollop of dill sauce.