Catlins Lake is a tidal upper estuary situated in the southeastern corner of New Zealand's South Island, approximately 6 km from the Pacific Ocean and about 2.5 km southwest of the town of Owaka. The lake spans nearly 2 km at its widest point and stretches roughly 4 km in length. It is formed where the Catlins River and the Owaka River converge at Pounawea before opening into this broader tidal basin. The Māori name for the area, Pounawea, translates to "the meeting place of the waters," reflecting the confluence of these two rivers at the lake's lower end.

As a tidal estuary, water levels and currents within Catlins Lake are governed by tidal cycles, which paddlers should account for when planning trips. The tidal nature of the lake means conditions can shift considerably depending on the state of the tide, and sea-run fish move through the system, indicating a meaningful connection to the open ocean. The lake is noted as a significant habitat for wading birds, making it of interest to those attentive to wildlife.

Access to the lake is available from the Southern Scenic Route along the north side, where a viewpoint pull-off is located. Lakeside Road skirts the southeast side of the lake and is described as suitable for fishing access, connecting further to Hinahina Road toward Jacks Bay. The Catlins River can be reached by crossing a bridge on the highway southwest of Owaka, offering a potential upstream paddling extension into the Catlins Forest Park area.

The wetland area surrounding the lake contains wahi taonga — sites of significance to Māori — including middens and other evidence of historical occupation, lending the area cultural weight beyond its natural character. The broader Catlins region is accessed primarily via the Southern Scenic Route, and the nearby settlement of Pounawea sits at the lower estuary where the rivers meet. Accommodation options exist in the immediate area, including a cottage directly on Lakeside Road beside the lake.