11. A waterfall from the mouth prevents fish migration between the upper and lower river. 12. During the summer months the dams increase their water releases to aid fish migration downstream. 13. A minimum amount of flow must be maintained in Dry Creek to allow fish migration . 14. The plant's development included a high-tech fish ladder intended to promote fish migration , especially salmon. 15. This great fish migration is called the sardine run. 16. Today Hells Canyon Dam is the first total barrier to fish migration on the Snake. 17. Impacts were to impede fish migration and to cause the accretion of sediment behind the weir. 18. In addition, natural fish migration patterns can be modified when certain areas of this route become uninhabitable. 19. The weir attached to Low Mill has a drop which is still a barrier to fish migration . 20. The third alternative was chosen two years later, but did not substantially improve fish migration as expected.
