Lets start with the basics. Salmon, also known as trout, are a type of fish that are anadromous, which means they migrate to feed and reproduce. Most salmon are born in fresh water, swim to the ocean, then return to fresh water to reproduce. The last stage of this process is called a salmon run, when the fish swim upstream in rivers to lay eggs on the gravel beds where they were born (using an invisible compass called magnetoreception). Once they lay their eggs, the salmon die off and the process begins again.
This all sounds pretty normal, right? There's one tiny detail I forgot to mention. Because of our hubris/desire to interrupt nature's processes/need for irrigation/whatever, humans have built dams all over the place. Sure, they can be useful for some things but they're a big pain in the a** for the salmon who are trying to swim to their gravelly breeding ground. Yes, salmon can jump, but not over a dam(n) wall.
But instead of letting a whole species die off (which we seem to be pretty talented at doing) the peeps over at Whooshh Innovations came up with a better idea: the Salmon Cannon.