Heat a large pan of lightly salted water until boiling. Cook the linguine according to the pack instructions, then drain and return to the pan, reserving a little of the cooking water.
Bring the white wine to the boil in a pan, stir through the crème fraîche and cook for 1–2 minutes, until reduced by half. Add the salmon to the pasta along with the crème fraîche sauce and lemon rind. Stir together, adding a little cooking water to loosen if needed and season to taste. Just before serving, toss through the watercress.