Lake Jasper is a permanent freshwater lake located within D'Entrecasteaux National Park in the South West region of Western Australia, near Pemberton. It is the largest freshwater lake in the South West of Australia, measuring approximately 4 kilometres in length and 2 kilometres in width, with a surface area of 4.5 square kilometres. The average depth is 3 metres, with a maximum depth of 10.3 metres. The lake sits on the flat Scott Coastal Plain, with a high dune ridge to the west and the Donnelly River to the east.

Canoeing and kayaking are explicitly supported activities at the lake, and power boats have been banned, meaning paddlers can explore the water without motorised vessel traffic. The lake is also noted as suitable for all passive watercraft. A shore-based boat ramp exists at the lake, though access is noted as having a difficult track. The campground, known as Lake Jasper (Yoondaddup) Campground, provides beach access to the lake and is accessible only by high-clearance 4WD vehicle. The campsite is located on the eastern side of the lake and includes seating facilities. Bookings are essential for the campground, and park entry and camping fees apply. No dogs or other pets are permitted within the park.

The lake is classified as a White Water Lake, a designation related to the low levels of tannic acid in the water, which results in notably clear water quality. The surrounding area supports extensive tall sedgeland and is recognised as one of the five most important wetlands for waterbirds in the South West, making wildlife observation a likely feature of any paddle. The lake and its two smaller neighbouring lakes, Lake Wilson and Lake Smith, are inhabited by all of the region's endemic freshwater fish species, including freshwater cobbler. Frogs and invertebrates are also present.

The campground is subject to a complete fire ban. The Department of Biodiversity, Conservation and Attractions conducts ongoing 1080 baiting in the area to control feral cats and foxes, which is relevant for anyone travelling with animals, though pets are already prohibited. The lake has evidence of ancient Aboriginal activity beneath its waters and holds cultural significance to the Bibbulman and Menang peoples, the Traditional Owners of D'Entrecasteaux National Park.