Salinity levels are variable, differing both between lakes and varying with the water level in the lake. Both Big Quill and Little Quill lakes have shallow shorelines of muddy or sandy alkaline flats. Middle Quill Lakes tends to be deeper, but in drought years also provides excellent mudflats and shallow water for staging and breeding shorebirds. The north and east shores of Big Quill Lake are very shallow. Renaud et al.
Similar conditions occur on the west side of Big Quill Lake and on Middle Quill Lake.
The south shore of Big Quill Lake and north shore of Little Quill Lake have fewer beaches or alkaline flats suitable for large concentrations of staging shorebirds. Adjacent marshy wetlands are also extremely important for migrating shorebirds, especially at night when they use such habitats for roosting. International Shorebird Survey operations in 1988 resulted in a total of 155,000 shorebirds being counted on Big Quill Lake, including an estimated 23,500 Sanderling. Surveys of all three lakes in spring 1993 provided a one day peak count of 197,155 shorebirds. The Quill Lakes have been designated as a Western Hemisphere Shorebird Reserve Network Endangered Species site.