Boil potatoes, eggs and fillets separately.
Peel cucumbers.
Finely chop the greens (5-6 twigs).
Cut potatoes, eggs, fillets and cucumbers into cubes, mix with herbs.
Mix mayonnaise and sour cream, then fill with water.
Add 1.5 tablespoons of salt and 1 tsp of citric acid (only add not all at once, so as not to overdo it).
Refrigerate for a couple of hours to infuse.