In Pale Moon's Shadow B3, there's a river that, if a player fails a DC15 athletics check, he floats ten feet down river. Pretty simple except, there's nothing stating the length of the river, or what happens if the player is carried further down. In the text blurb at B2, it states there's a waterfall, and the provided map also shows the river that the PCs cross is connected to the waterfall, but there's no listed height to it.
I was GMing a Cleric and a Paladin (third guy dropped out last minute) and the Paladin made it safely across, but the Cleric had a solid -6 to Athletics and literally couldn't pass the check save for rolling two 20s. I arbitrarily stated they were 80ft up the from the waterfall, and that it was a 1d100ft drop. The Cleric managed to fail all 24 swim checks (three per round), and half-way through decided to climb back up to where he was, so I let him use his reaction to Grab Edge with an Easy DC11. He failed all those, too.
Mind you, the paladin was throwing a rope to him the whole time, which I ruled to be an Aid Another action.
So Pavlov the Cleric fell 48 feet into into the water below, and was stuck 1d50ft (30) below the surface with 10 breath units. He was still underneath the waterfall, so it made sense to me that he still needed the DC15 swim checks. That means he needed to succeed six times, or critically succeed three times, without critically failing. Don't forget his -6 to Athletics.
The paladin leaped in after him, taking the fall damage, and managed to Aid Another him up to 15ft below the surface before he ran out of breath, rolled a 5 on his Fortitude save, and instantly died.
The moral of the story is that if you're wearing heavy armor, train athletics.