The Colorado and Ohio rivers are among the 'most endangered' in America. Here's why

Growing up, Pittsburgh native Judy Baumgartner saw big plastic pipes from industrial plants going into the Ohio River.

This was during the 1960s and 1970s, when industrial plants still dominated the city's waterfront. Pittsburgh's steel, coal, petroleum and other industries had long sustained the local economy, but they also released pollution into the water.

Baumgartner still remembers the smell.

"It had a sweet, different smell. It wasn't fresh water," she said. "But, you know, you just got used to it."

Many of those industries have largely disappeared. Baumgartner, however, assumed the Ohio River was in good health.

"To me, the river looks a lot more healthy now than it did back then," Baumgartner said.

The Ohio River forms in Pittsburgh's backyard, where the Allegheny and Monongahela