I am in no way defending Seattle City Light but salmon redds can be dry for a certain amount of time.
All species are differnt on which how long their redds can be 'dry'. Dry is a relative term because even if there is no river water flowing over the gravel in which the redds are deposited there is still a certain amount of water within the gravel. Depending upon the age of eggs is also a factor which determines the mortality that the eggs occur when the redds become dry. Very early in the egg's life, an egg is more likely to survive ebing 'dry'. At this time very little cells have devolped so they for one require very oxygen and secondly there is a much larger surface area ration of membrane to 'insides'. I hope this makes some sense ...and again I am in no way defending Seattle City Light but I am just adding some optimism to this grim circumstance.

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Ryan S. Petzold
aka
Sparkey and/or Special