Somebody cut a shortcut into a riverbank, and the river took it.

By 1904 silt had clogged the canal carrying Colorado River water to the farms of California’s Imperial Valley, and the agricultural miracle that had been sold to settlers was dying in the fields. Engineers opened a temporary intake downstream to keep the water moving. That worked until winter. A run of floods through 1905 tore the makeshift opening wide, and the river, offered a choice between its old bed and a straight drop into a basin below sea level, went for the drop.

It kept taking it for roughly two years.

A lake nobody ordered

The numbers are hard to hold in your head. At the peak of the break, water was pouring into the Salton Sink at tens of thousands of cubic feet per second, carving fresh gorges out of desert floor as it went. Southern Pacific Railroad watched its track disappear under the rising water, and E. H. Harriman, the company’s president, went to President Theodore Roosevelt for help, as documented by EARTH magazine. Thousands of men and trainloads of rock eventually shoved the Colorado back into its channel in February 1907, per the timeline maintained by the Salton Sea Authority.

What was left behind stretched roughly 58 kilometres long and 42 wide. California had its largest lake, and nobody had ordered one.

Everyone assumed the desert would take it back. Federal officials were confident enough that in 1909 they reserved a further 10,000 acres of land under the water in trust for the Torres Martinez Band of Desert Cahuilla Indians, on the understanding it would be dry ground again by the 1920s.

Farm runoff kept it alive, then stopped

Instead the lake got a steady drip feed. Water used to irrigate Imperial Valley fields had to drain somewhere, and the only ground lower than the fields was the lake. Agricultural runoff propped up the water level for most of a century, long enough for the shoreline to grow marinas, yacht clubs and a passing association with Frank Sinatra.

Then the maths changed. Farms got better at not wasting water, Colorado River allocations tightened, and a hotter climate pulled more off the surface every year. Less in, more out, and the shoreline began walking backwards. Around 16,000 acres of lakebed have been uncovered over the past two decades, reports the University of Southern California. That’s a great deal of newly bared ground with nothing holding it down.

Efficiency is the right policy. It is also the thing draining the lake, which is the sort of knot water management keeps tying for itself.

What the wind lifts off the lakebed

Exposed lakebed is called playa, and this playa has been collecting whatever the valley drained into it for a hundred years. Fine sediments laced with selenium and arsenic, deposited by farm drainage and by local geology, sit on the surface waiting for a windy afternoon, as summarised in a Congressional Research Service report. Imperial Valley gets plenty of windy afternoons.

Working out exactly what in that dust does the damage has been harder than it sounds. A team at UC Riverside led by David Lo went looking for it by piping aerosols from the lake into exposure chambers holding mice. Their result, published in Science of The Total Environment and described by the university, was that Salton Sea aerosol switched on a distinctly non-allergic kind of lung inflammation, unlike the response to a common household mould. Mice given Pacific Ocean aerosol did nothing much at all. Lo’s suspicion is that the culprit is microbial material dissolved in the water rather than the heavy metals everyone expects.

That is one laboratory study in mice, and Lo has been careful to say it doesn’t settle what’s happening in human airways. Call it a lead worth chasing.

What it has already done to a generation of lungs

The human evidence is separate, and it is grim. Researchers at the Keck School of Medicine of USC followed 369 children in the valley for about two years, measuring how much air they could force out of their lungs and how fast. Kids living within 11 kilometres of the shoreline gained lung capacity more slowly than kids further out, at a rate the school compares to living within 500 metres of a freeway. That study was published in JAMA Network Open. Earlier work from the same group found more than one in five local children have asthma, close to triple the national rate.

Lungs do most of their growing in adolescence and then peak. Miss the growth spurt and there is no second attempt.

Hay bales, ponds and a lithium boom

California’s response has been to try to hold the dust down rather than refill the lake, because there is no spare river. Hay bales get staked across open playa to break the wind. Shallow ponds get flooded over the worst of it. State agencies running the Salton Sea Management Program have been building engineered wetlands along the southern shore, both to trap sediment and to give migrating birds somewhere to land.

Meanwhile the brine under the lakebed turns out to hold enormous quantities of lithium, and an industry has arrived to argue about how to get it out. Extraction plants mean jobs in one of the poorest counties in California. They also mean trucks, and trucks mean more dust on the same roads, past the same schools.

The accident took eighteen months. The consequences have had a century, and the children in that lung study are teenagers now, carrying capacity they were never going to get back.