The Delaware River watershed was once so toxic it killed fish, and could be smelled by pilots from 5,000 feet up, writes Michaela Winberg for the Philadelphia Inquirer.

But it’s been 50 years since the Clean Water Act was implemented.

Today, experts note the river is the cleanest it’s been in decades, but not enough to swim in.

The Delaware River Basin Commission indicates the Philly section of the river, EPA’s Zone 3, has nearly four times the sewage than anywhere else.

“The fertilizer, dog poop, herbicides and pesticides that end up on our landscape because of the way people live their lives — that gets collected by the stormwater system and ends up in the river,” said Maya van Rossum, of the Delaware Riverkeeper Network.

Philadelphia is the only spot along the Delaware River deemed unsafe by the EPA. It’s OK, though for boating, kayaking and some light wading near the shore.

The remaining sections in both directions are safe enough for “primary recreation,” like swimming.

The Delaware River Basin Commission has launched a bacterial monitoring program in Zone 3. If they find the water is clean enough for primary recreation, they’ll ask the EPA to switch designations.

Read more about the Delaware River’s status here.

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