Percy manipulates Rivers and Acheron Effects

"Percy gave them as much cover as he could—causing blood vessels in the ground to
burst one after the other. Some monsters were vaporized in Styx water. Others
got a Cocytus shower and collapsed, weeping hopelessly. Others were doused
with liquid Lethe and stared blankly around them, no longer sure where they
were or even who they were."

- Doors of Death, Chapter LXXI (Annabeth), Pg. 381

"‘Sometimes ... Sometimes when souls arrive in the Underworld, they
have done such horrible things that they’re not even fit for the Fields of
Punishment. They have to be cleansed ... in the Acheron.’
	Will cupped his sun globe a little tighter. ‘And I guess this cleansing is
... painful.’
	‘The pain is not just physical,’ said Screech-Bling. ‘It will rip your soul
to pieces. It will find every bad thing you have done, every bad thought,
and make you feel agony and guilt until you have been purified.’
	Will gulped. ‘And then ... you can get out?’
‘Oh, no,’ Screech-Bling said. ‘By then you will have dissolved into a
fine sediment of eternal misery, still conscious, but probably not sane.’
	‘Even standing on the banks of the Acheron will affect you,’ Hiss-
Majesty warned.

- The Sun and the Star, Chapter 26, pg. 218-219