About the fishes migratory problem...

When was this plan to build the dam started?

When was this plan to build the dam started?

Could it be after seeing the previous dam?

For the Kappa, they also would like to have a stable and bountiful supply of water which is easily accessible.

Not really.

This plan has been in the works since a very long time ago...

This plan has been in the works since a very long time ago...

Using the pre-assigned fish route would solve the problem.