The Onyx River
Antarctica does have the Onyx, a seasonal meltwater stream that typically flows for about 6–8 weeks during the austral summer. That is roughly 42–56 days, so “about 60 days” is a reasonable rounded figure, not a fixed duration every year.
The stream is over 30 km long, running from Wright Lower Glacier to endorheic Lake Vanda in Wright Valley. Its season and discharge vary with summer melt; long-term measurements show that season length has changed over time. Here, “river” is the familiar name for a seasonal glacial stream, not a year-round river.