Redd excavation

Most salmon, trout, and charr bury their eggs in a gravel nest called a redd. A female excavates her redd by turning on her side and vigorously undulating her body which may involve some forward and upward swimming motion. Upward motion is restricted when spawning in very shallow water (depth much less than a body length) suggesting that the surface functions as a backboard. In deeper water the female will move forward at a steeper angle. The female will finesse larger sized pebbles into the center of her redd. She assesses her progress by probing: https://www.salmonography.com/Salmonid-Topic/Probing-behavior/