Many landowners are in the process of identifying and implementing mitigations to reduce diffuse contaminant loss to surface waters, under regional limit-setting processes required by New Zealand’s National Policy Statement for Freshwater Management (NPS-FM). Constructed wetlands (CWs) are increasingly being considered as part of the toolbox of mitigation options available to meet limits. However, research is needed to better quantify their environmental performance and benefits, so that landowners can claim expected contaminant load reductions and regulators have confidence that specific wetland mitigations will deliver the reductions to on-farm contaminant budgets, required to meet catchment load objectives. This is expected to promote their adoption by land owners and facilitate regulatory acceptance. Here we outline a collaborative research programme aimed at developing sufficient guidance and certainty of expected contaminant reductions to enable farmers and regulatory agencies to account for constructed wetland effects within farm nutrient management plans and regional planning responses to the NPS-FM. New Zealand and relevant international experience with farm-scale constructed wetlands will be over-viewed and knowledge gaps limiting wider application identified.