Projects assessed as having the potential to adversely affect the environment can gain approval with the caveat that monitoring will be undertaken. The implications from such a decision are that adverse findings from monitoring will lead to the project at least, being subject to measures mitigating adverse impacts identified by the monitoring. With regard to the platypus, detection of adverse impacts by a monitoring program can be constrained by both limitations on the sampling techniques currently available (observations and/or capture by netting and/or assessment of important habitat variables) and by the nature of the data these sampling methods can provide. Capture techniques are the preferred method but capture using mesh (‘gill’) nets is limited by stream flows and the presence of fish and/or large woody debris (‘snags’). Fyke netting, the other preferred method, is largely restricted to being used in small water bodies. Low numbers and variability of both captures and observations of the species in the wild are common limitations to the statistical adequacy of a monitoring program for the platypus. These constraints must be raised in the environmental impact assessment process so that decision-makers are aware that, depending on the species, monitoring programs may not necessarily be able to detect adverse impacts or separate human-induced impacts from those affected by natural perturbations. Approval with the precaution of monitoring should be made only if it can be concluded that the proposed monitoring study has the capacity to detect any adverse effects of the project and, in the instance that such adverse effects are detected, that these can be reversed or mitigated.