It is. With 2.2 mg of iron per 100 g, raw watercress certainly makes it into the top league of healthy iron-rich vegetables. Only raw parsley, mint and lentils have more iron, and spinach has less. Watercress is only really at its best when the leaves are absolutely fresh and vivid dark green so avoid any with traces of yellowing. To keep watercress fresh, store it with the leaves submerged in a bowl of cold-water - easier if you buy it in a bunch, not loose.
** Asian Recipes