Why is there white stuff on my baked salmon?

The answer

The white substance is albumin, a protein that moves to the surface as the fish cooks and sets there. It is harmless. A small amount is normal, but a lot usually means the oven was too hot or the bake ran long. Cooking at a more moderate temperature, pulling the fish as soon as it flakes, or soaking it briefly in a salt brine beforehand can reduce it.