Lake Monowai is a glacially carved lake in Fiordland National Park, located about 67 km from Te Anau (approximately one hour by road) and 120 km from Invercargill (about one hour and 45 minutes). The lake is roughly boomerang-shaped in plan, approximately 12 miles long and up to one mile wide, covering around 11 square miles, with a maximum depth of 520 feet and a surface elevation of 643 feet above sea level. The surrounding forested mountains and multiple inlets and bays give the lake a varied, exploratory character.

Access for paddlers is at the end of Lake Monowai Road. The boat ramp and associated facilities are managed under a Right to Occupy Agreement between Fish & Game and Pioneer Energy, which owns the land. A jetty construction and boat ramp restoration project was underway as of early 2025 to improve launching and landing conditions.

A key hazard throughout the lake is submerged tree stumps along the shoreline, which pose a real risk of puncturing or damaging a vessel. Paddlers should choose landing spots carefully and remain alert in shallow areas. Wind can also be a significant factor; conditions can deteriorate and make progress slow and cold, particularly in the upper reaches of the lake.

Didymo (Didymosphenia geminata) is present in Lake Monowai. All vessels and gear that have been in contact with the water must be checked, cleaned, and dried before and after use. Paddling up any tributary rivers from the lake is not permitted, as those waterways are didymo-free.

Several huts are accessible by water, making the lake well-suited to multi-day trips. Rodger Inlet Hut (also referred to as Roger Inlet Hut), Eel Creek Hut, and Monowai Hut can all be reached by paddling. A walking track connects Borland Road to Monowai Hut, offering a route that can be combined with a paddle for a circuit. One trip report describes a paddle from Monowai Hut down the lake, stopping at Eel Creek Hut after roughly two hours, then crossing to the other side and rounding Tangney Bend and Shelter Point to reach Rodger Inlet Hut. The lake also provides access to tramping and climbing objectives in the surrounding ranges.

The lake's name is thought to derive from an earlier Māori form meaning "channel full of water," as noted by the surveyor-explorer James McKerrow, who recorded it in the 19th century.