Resumo. Abstract Accurate impact evaluations of different interventions are paramount in environmental sciences. In this context, the main challenge is to identify causal relationships to understand how different interventions affect the systems of interest. For this task, the counterfactual thinking can be used to estimate the impacts of interventions on the real scale of the problem using observational data. By definition, counterfactuals are states contrary to facts. In the context of interventions, they are the states of the units of analysis in the absence of intervention. This approach allows one to estimate the impact more accurately by comparing the differences between factual and counterfactual states. In this essay, we present some basic elements of the counterfactual thinking and discuss how it, based on experiences in other areas (e.g., medicine and economics), may be useful for the research of complex problems in aquatic ecology.