Williams, W.D. (University of Adelaide, Department of Zoology);

Lake Corangamite in western Victoria, Australia, is the largest permanent lake on the Australian mainland. Its levels and salinities fluctuated naturally until recently. Since about 1960, its major inflow creek has been diverted for management purposes and lake levels have fallen and salinities risen. The changes have been most profound since 1980. Since 1980, salinity has risen from ∼35g/L to >50g/L, water levels have fallen by nearly 2m, and many islands have become peninsulas or have disappeared. The major effect has been a change in the composition of the biota from one that is characteristic of lakes in the region of moderate salinity (>35g/L) to one that is characteristic of more saline lakes (50-100 g/L). In particular, Austrochiltonia subtenuis (Amphipoda), Coxiella (Gastropoda), Galaxias maculatus (Pisces) and Ruppia (macrophyte) have almost disappeared. The loss of these species has greatly decreased the value of the lake to the avifauna in particular and as a natural resource in general.

The changes to Lake Corangamite resulted largely from the diversion of the inflowing waters from the Woady Yaloak Creek, the major influent stream, into the Barwon River. The diversion scheme, undertaken by the Rural Water Commission of Victoria, was implemented mainly to minimize the possibility of flooding of land adjacent to the lake. The environmental consequences of such diversion were not fully considered. The paper documents the physico-chemical and biological changes that occurred up to 1992, and discusses issues of conservation and management interest associated with the changes. Changes in the level of Lake Corangamite and associated limnological features accord with the pattern observed in many salt lakes worldwide.

Salt lakes respond more sensitively to climatic and other changes than do freshwater lakes. Water levels and salinities of Lake Corangamite Vic, the largest salt lake in Australia, had fluctuated naturally until diversion of its major inflow, Woady Yalouk Creek, in 1960 to minimize flood risk to adjacent land. Since 1980 salinity has risen by 15g/L, water levels have fallen by 2m and many islands have disappeared. Physicochemical and biological changes in the period 1960-92 are documented and conservation issues discussed. The major effect has been change in biota. In particular, the amphipod Austrochiltonia subtenuis, the fish Galaxias maculatus and the macrophyte Ruppia have almost disappeared, decreasing the value of the lake as a habitat for water birds and as a natural resource. It is suggested that restoration to original salinity by substantial water release from the creek could lead to restoration of former biological status.

Victoria, Salinity Control Program