The Salton Sea is about to start shrinking more rapidly. A 2003 water transfer deal called for the Imperial Irrigation District to deliver “mitigation water” to the lake for 15 years. With those water deliveries ending in the final days of 2017, the lake’s decline will begin to accelerate. More than 19,000 acres of dry lakebed have already been left exposed as the shorelines have retreated over the past two decades. And as the lake continues to shrink, more lung-damaging dust is expected to spew from the growing stretches of lakebed into communities that already suffer from high asthma rates.