While in the US last year one of the places I visited was the Nimbus Fish Hatchery in Folsom, CA. A fascinating place it was. Dams, like the Folsom Dam and the Nimbus Dam built along the American River to meet the water needs of the growing population in the region prevented salmon and steelhead from reaching their natural spawning grounds in the upper reaches of the river.
As a result the salmon and steelhead population was diminishing. The Nimbus Fish Hatchery was established to maintain the populations of these fish along the American River. The hatchery is a local attraction where families go for a visit. During Autumn families flock to see the annual migration.
So you think you have problems? The fish, trying to swim upstream to fulfill their natural urge for multiplying, are physically blocked from by huge gates lowered across the river. They are encouraged and re-routed to these fish ladders where they flap their way, painstakingly slowly, up each of these stairs. We witnessed a salmon come into the first step, and step by slow step, and jump to the next one. There are 20 of these steps. As he made it up each step, we walked up the side to keep up with him. By the time he made it to the top he was tired. The higher he got the slower he became.
The harvested eggs are hatched and raised in large tanks, and when the fish are big enough, they are released back into the river to start the cycle of life.
I guess that they will eventually, in the future, find themselves climbing the fish ladder.