Remedial action is often studied and embarked upon without consideration of the repercussions - possibly negative - of such action. For example, the damming of a river may eliminate floods, make irrigation possible, and employ hundreds of people; but unforeseen are such consequences as the lost nutrients which once collected in the river and fertilized the plain when the river overflowed; the fish that subsequently have no nutrients to feed on, threatening the local fishing industry; and the costs of re-employing and re-housing the now unemployed fishermen.