Lake St Lucia is one of Africa's largest coastal lakes, and is one of South Africa's most important wetland ecosystems. However, like many ecosystems, it is under threat from increased demands for water in its catchment area. Reduced runoff primarily impacts on the salinity regime of the lake. At low lake levels there is a net inflow of seawater to the lake. Evaporation concentrates the salts, and lake salinities rise to several times that of seawater. In water periods, lake levels rise and there is a net outflow toward the sea. Under these conditions salinities are low. The lake therefore naturally experiences a range of salinities associated with wet and dry cycles. Increased water use in the catchment will, however, impact on this natural salinity regime. This paper introduces a suite of models which will be used to facilitate management of the water resources of the catchment. The preliminary work presented demonstrates the ability of the models to provide meaningful input into a catchment management decision-support system.

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