Risks and uncertainties arising from climate change are increasingly recognized as significant challenges for water governance. To support adaptive approaches, critical examinations of water policy practices and rationalities are needed. This paper focuses on the treatment of climate change in Australia’s Murray–Darling Basin (MDB) reforms over the past decade. While the MDB faces potentially significant drying trends due to climate change no reductions in future water availability due to climate change were formalized in the 2012 Basin Plan — a regulatory instrument agreed to by Australia’s National Parliament. The background, key dimensions and possible reasons for this decision are examined. Possible reasons for not formally reducing water deemed available in the future include the complexity and uncertainty of climate science, the cultural construction of “climate normal” based on long-term averages, and institutional settings that reinforce dominant “hydro-logical” approaches and rationalities. Minimizing the political, legal and financial consequences of attributing reductions in water allocations to climate change are also potential reasons. The case of the MDB, as outlined in this paper, demonstrates some of the ways climate change is causing systemic challenges for adaptive water governance, and that innovative approaches need to be embraced, including better processes for institutionalizing science/policy integration.