Passenger pigeons were once the most abundant bird in North America. But in 1914, they went extinct. Most of their last nesting grounds hugged the Great Lakes. What was it like to experience these birds? And what are we left with when we lose a species?

Owls are elusive birds of the night – part of this mysterious world we rarely encounter. Researchers are learning just how complex an owl’s communication is. We go into the woods to try to experience these birds for ourselves.

On April 3, 1851, a man who escaped slavery to Boston was kidnapped by slave catchers. The Fugitive Slave Act turned cities across the North into hunting grounds. But resistance was growing. In Pennsylvania, William Parker was building a network to fight back.

When Seth Swoboda’s trees started dying, he asked two scientists for help. Their theory: herbicides were drifting onto his private property from farm fields and killing his trees, and it was happening all over. They just had to prove it.

After a boat captain notices strange black goo on his ship’s rudder, he scoops some of it into a cup. A few months later, that cup ends up in a lab, where scientists make a surprising discovery.

In northwest Indiana, there’s a 20-mile stretch of Lake Michigan that’s dominated by industry. It’s some of the dirtiest water in the lake, but it's also home to some of the biggest waves anywhere on the Great Lakes. Despite the pollution, there’s a dedicated group of surfers who keep flocking to this area. And one day, after a really big chemical spill from one of the factories, the surfers decide to do something about it.

Kevin Shafer is obsessed with rain. As the head of the Milwaukee Metropolitan Sewerage District, it’s his job to be. But when a thousand-year storm comes out of nowhere and dumps over a foot of rain, Kevin is faced with a decision: send sewage into people’s basements or into Lake Michigan.