Pennsylvania

It would mark the first time since 1967 that the EPA raised the bar for oxygen levels along the Philly stretch, essentially bring the Philadelphia stretch up to standards the rest of the river enjoys.

The biggest contributor to low oxygen rates is wastewater-treatment plants, particularly nine key plants along the river, including those owned by the Philadelphia Water Department (PWD). The plants release treated wastewater into the river. The wastewater contains ammonia, which can come from meat, blood, urine, and cleaning products. Ammonia eats up oxygen in the river as it converts to nitrate. That leaves less oxygen for fish.

If the EPA rule proposal is approved, plants operated by Philadelphia, the Camden County Municipal Authority, and Wilmington would all have to comply with new permitting overseen by the state DEPs in coming years. The plants were built decades ago without a way to get rid of the large amounts of ammonia in human waste.