How many months a year does the Onyx River flow in Antarctica?

The Onyx River is an Antarctic meltwater stream which flows westward through the Wright Valley from Wright Lower Glacier and Lake Brownworth at the foot of the glacier to Lake Vanda, during the few months of the Antarctic summer. At 32 kilometers (20 mi) in length, it is the longest river in Antarctica.

The Onyx River flows away from the ocean, an example of endorheic drainage, as the Wright Lower Glacier blocks the mouth of the Wright Valley. It has several tributaries, and there are multiple meteorological stations along the length of the river. Flow levels are highly variable, both during the day and between summers, with the river failing to reach the lake some years. In contrast, it can cause significant erosion in flood years, and was rafted in 1984 by New Zealand researchers. At one time, the river's discharge reached 20 cubic meters per second (700 cu ft/s).

There are no fish in the Onyx River, but it supports microscopic life, and the algal blooms can be quite extensive. The environment consists mainly of cyanobacteria and other algae. A few micro-animals (nematodes, tardigrades, and rotifers) live in the river. Skuas are also occasionally present in the area.