In a large saucepan, melt butter over medium heat. Add onions and sauté 5 minutes or until soft.
Add 1 1/2 cups water, potato, salt and pepper. Bring to boil, reduce heat and simmer, covered, 10 minutes or until potato slices are fork-tender.
Bring chowder to boil. Stir in salmon, reduce heat and simmer 3 minutes or until fish flakes easily when tested with fork. Stir in milk and simmer until fish chowder is heated through (do not boil). Sprinkle with dill or parsley and serve.