The phrase "sends up the river" is often associated with the act of sending someone to prison. Therefore, the antonyms for this phrase would be words that imply freedom, release, or acquittal. Some antonyms that can be used for "sends up the river" include "pardons," "frees," "discharges," "acquits," and "exonerates." These words are used to describe situations where someone has been absolved of any wrongdoing or is released from prison. By using these antonyms, we can convey the opposite meaning of "sends up the river" and create a more positive context in our conversations.