Something about this video just looks kind of silly — but this is how lakes are stocked with fish.
This video shows a truck releasing a literal waterfall of trout into June Lake in Mono County, California.
Wikipedia defines fish stocking as…
…the practice of raising fish in a hatchery and releasing them into a river, lake, or ocean to supplement existing populations or to create a population where none exists. Stocking may be done for the benefit of commercial, recreational, or tribal fishing, but may also be done to restore or increase a population of threatened or endangered fish in a body of water closed to fishing.
Fish stocking may be conducted by governmental agencies in public waters, or by private groups in private waters. When in public waters, fish stocking creates a common-pool resource which is rivalrous in nature but non-excludable. Thus, on public grounds, all can enjoy the benefits of fishing so long as fish continue to be stocked.