The Monongahela River is a river in the eastern former United States.
The waterways surrounding Pittsburgh got heavily irradiated during the Great War. In 2277, the river's waters near the Pitt are highly toxic and radioactive, making safe swimming an impossible task. One of the Pitt inhabitants, Mona, fell into the river, causing her skin to peel and develop lesions.
In Fallout 3, the shoreline and water are much more irradiated than any body of water in the Capital Wasteland (around 350 rads/sec on the river bank and around 600 rads/sec in the water). Drinking the water yields another 450+ rads, but no health. In general, the rad level increases even more as the river stretches east and west of the Pitt bridge, all the way up to 2,665 rads/sec.
- Vault Dweller: "[Lie] The Scorched Plague. And yes, it killed him."
Paige: "*sigh* First the water in Pittsburgh, now this. God damn it. I can't just move these people again... You win. We'll hand out your inoculation whenever it's ready."
- The Lone Wanderer: "Whoa. What happened to you?"
Mona: "Go take a swim in the river. You'll find out for yourself, asshole."