Salmon are famous for their epic migrations to and from the ocean, but their natural rhythm has been disrupted by recent drought conditions in California. Following the state's driest year since records began, Californian authorities have found it necessary to actually transport smolt (juvenile salmon) on trucks to the delta of the Sacramento River. That's instead of releasing them from the hatcheries directly into the river where the adolescent fish would make the trip themselves.

As Bob Clarke of the US Fish and Wildlife Service explains, the lack of rain has made the journey to the ocean perilous for the salmon, with the river liable to be "too low, too slow and too clear." The present effort to get the young Chinook salmon to their destination safely has precedent as far back as 1991. One of the lessons learned from the earlier transporting was that simply dumping the fish at the river banks would feed awaiting predators, so now there's a much more sophisticated method for introducing the smolt to the river — including accounting for water temperature and conditions.

Like Free Willy without the killer whale

While there are some fears that the fish may struggle to return to their home waters when it's time to respawn — owing to not having made the outward swim themselves — the authorities see that risk is the lesser of two evils. The outcome of this human assistance will be known in three to four years when it's time for the salmon to make their return. A quarter of all the trucked fish has been tagged and identified, so researchers should be able to accurately measure how helpful this intervention has been.