The Southern Wide-field Gamma-ray Observatory (SWGO) will be a next-generation high alti-tude gamma-ray survey observatory in the southern hemisphere consisting of an array of watercherenkov detectors. With its energy range, wide field of view, large duty cycle and location itwill complement the other existing and planned gamma-ray observatories. In this contribution wedescribe the lake concept for SWGO, an alternative to a HAWC-like design with individual watertanks and a LHAASO-style design with artificial ponds. In the lake concept, bladders filled withclean water are deployed near the surface of a natural lake, where each bladder is a light-tightstand-alone unit containing one or more photosensors. We will give an overview of the advantagesand challenges for this design concept and describe the first results obtained from prototyping.