To make the salmon: Combine all ingredients except the salmon in a medium skillet or saucepan. Bring to a boil then reduce to a simmer. Season the salmon with salt and pepper on both sides, add to simmering liquid, and cover. Cook for 5 to 8 minutes or until just done.
To make the vinaigrette: Whisk together the olive oil and citrus juices, add the dill, and season with salt and pepper, to taste.
Toss the watercress with 3 tablespoons of the vinaigrette and season with salt and pepper, to taste. Arrange the watercress on a large platter and place the salmon in the center. Drizzle with additional vinaigrette and garnish with dill.