The booby prize this year for Dirtiest City in America goes to Fresno, California. This Central Valley city suffers some of the worst air in the nation, and a water supply so degraded that the city used to tell pregnant women not to drink from the tap. Fresno epitomizes the environmental challenges of the Golden State. And it’s not alone. Plenty of its neighbors in central California like Modesto, Stockton and Bakersfield have it almost as bad. (Other California metro areas ranked among the 20 Dirtiest Cities include San Jose, Riverside and Los Angeles — but don’t worry, they have lots of company from towns in the Midwest and on the East Coast, too.)

The environmental degradation of the Central Valley has many contributing factors. First of all, its geography doesn’t do it any favors. It’s a big, long bowl surrounded on three sides by mountains that trap pollutants from cars and factories and oil fields in an inversion layer.

Second, it’s a victim of what brought people there in the first place — rich fertile soils from which grow much of America’s fruits and vegetables. For decades farmers would burn leftover cuttings from their fields after the harvest — dumping massive amounts of lung-choking particulate matter into the air. Burning has been banned since 2004, and the air has gotten cleaner since then, but there’s still a long way to go. Compounding the problem are frequent dust storms, exacerbated by water shortages.

Third, all that agricultural activity has wreaked the Valley’s groundwater. Decades of fertilizer and pesticide applications and manure from livestock have caused noxious chemicals to trickle down into the water table. When pumped back up into homes, the water regularly gives people rashes when they shower in it. Nitrates in the water can cause babies who drink it to come down with potentially fatal “blue baby syndrome.”

What’s troubling is that rather than getting better, the water problem might be getting worse.