For decades, millions of gallons of raw sewage and trash have flowed from the Tijuana River to the Pacific Ocean, fouling beaches, angering Southern Californians and getting worse by the year.

An estimated 143 million gallons of waste from Tijuana spilled into the river valley in 2017, overwhelming a treatment plant built by the United States and Mexico nearly 25 years ago. Last October, a corpse clogged a sewage intake screen, causing a backup and sending 14.5 million gallons of polluted water over the border and into the U.S.