A project to protect Californians who live near the Salton Sea from deteriorating air quality could sink or swim based on the outcome of a June ballot measure. Proposition 68 would allow the state to borrow $4 billion through bonds to fund parks and environmental protection projects, including $200 million for a plan to preserve the rapidly shrinking Salton Sea. California’s largest lake has been evaporating since San Diego’s regional water agency stopped sending it water this year. Falling water levels increase the lake’s salinity and expose thousands of acres of dusty lakebed, which wind sweeps into nearby farming communities.