With the increase in population and industrial development, the utilization and management of water resources have become critical issues.

Large dams are widely constructed for water supply, irrigation, and power generation to meet people's needs. However, while these dams address water resource issues, they also negatively impact the ecological environment, one of which is the obstruction of fish migration and breeding.

During the construction of dams, the natural state of rivers is altered, creating a massive barrier. This makes it difficult for many fish species to pass through, significantly affecting their migration and breeding. Many fish species require long-distance migration, including upstream and downstream migrations and spawning migrations. However, the blockade of dams prevents them from migrating freely, resulting in a decrease in fish population and species diversity.

To address this issue, people have designed a type of engineering facility called a fish ladder.

A fish ladder is a passage for fish migration, which is a remedial measure taken due to human activities disrupting fish migration routes, generally by constructing artificial channels on dams or weirs to protect fish habits.

Fish ladders provide a detour route for migrating fish, allowing them to bypass the dam blocking their path. This sounds simple, but when you try to imagine such an intricate device, you may conjure some exciting images.

How could a fish climb the ladder steps? Imagine this: a series of ascending pools, not climbed by steps but rather by swimming against the current. Fish leap over the torrents of waterfalls, rest in pools, and then repeat the process until they have passed over the dam.

How are fish ladders designed?

Designing a fish ladder requires a lot of work. Several factors must be considered, such as the height and grade of the pools, the number of pools, their size, and the size of the water flow.

Fish ladders are not one-size-fits-all—they must be tailored to the fish using them. For example, trout and salmon have intense swimming speeds, which means they can swim in stronger currents than other species. However, you can't make the flow too weak, as a trickle won't attract fish to the passage's entrance.

However, fish ladders are not foolproof. Sometimes, fish find it difficult to locate the entrance, and long fish ladders can flush fish out, preventing them from reaching the top. Additionally, while the design purpose of fish ladders is to bring fish to spawning grounds, they may not offer protection to juvenile fish downstream. Juvenile fish may be caught in turbines without built-in protection, resulting in injury or even death.

Because not all fish ladders are practical, some interest groups argue that removing dams is better than constructing passageways. Demolition is not always an option, especially if the electricity generated by the dam is crucial to existing infrastructure. Still, some places find that removing a redundant dam is much cheaper than constructing a fish ladder.