Ocean-based salmon farming, as presently practiced, is thought to pose an existential threat to what we today think of as wild salmon. This raises ethical questions about, first, the value of wild salmon, and, second, the value of wild salmon of the particular type that exists today. This essay uses the debate around ocean-based salmon farming as a case study of ‘irreversible damage,’ a concept that figures heavily in environmental laws and regulations, in particular, in the so-called ‘precautionary principle.’ It is argued that although ocean-based salmon farming may, on the surface, seem to be a prime example of a threat of irreversible damage, a wish to avoid irreversible damage does not support banning such farming. In contrast, it is argued that concern for irreplaceable value might support a ban. The findings suggest that it often would be appropriate for environmentalists and conservationists to focus more on irreplaceable value and less on irreversible damage.