I’ve often written about the ways in which our rivers in the western United States have become like plumbing (and here, here, and especially here). But one of the most interesting things to me about metaphors is when you push them to too hard. You can learn a lot at the point where the metaphor breaks down.

So what does it tells us about the nature of the California “plumbing” system when, as Matt Weiser reports, they have to drive salmon to the ocean in trucks?

On Monday, state and federal wildlife officials announced a plan to move hatchery-raised salmon by truck in the event the state’s ongoing drought makes the Sacramento River and its tributaries inhospitable for the fish. They fear the rivers could become too shallow and warm to sustain salmon trying to migrate to sea on their own.