My Girlfriend is a Biologist working for fisheries Canada, according to her, studies were showing very little fish movement over the weir so all the fish from the weir to Bearspaw were basically trapped and only breeding amongst each other creating a very poor gene pool. By opening up the weir one of the effects is the fish can now easily travel up and down the river, Biologists are expecting the fish quality in this section of the river to improve significantly . However according to her you won't notice and changes for a couple years
P.S. almost forgot. she is also expecting the lower elbow to see improved fish quality as a direct result