A series of pollution control measures have been introduced to protect water quality in the Olifants river basin, the third most water-stressed and most polluted basin in South Africa. This paper employed an environmentally extended computable general equilibrium (CGE) model to analyse the economic and environmental implications of a tax on water pollution in the basin. Implications of increasing the pollution tax rate currently in place for the levels of economic activities and water quality have been simulated under alternative tax revenue recycling schemes. Results of our policy simulations suggest that internalising the cost of water pollution through the tax regime achieves its environmental goals of protecting the aquatic ecosystem, by shifting production away from pollution-intensive sectors. This, however, comes at some cost to the regional economy of the basin. Recycling the tax revenue through income transfers to households or a subsidy to pollution abatement mitigates the adverse economic impacts.