Citizen science has a problem with engaging diverse participants, with a growing number of studies showing those most marginalised in society, who could benefit most from citizen science activities, are the least likely to participate. The full implications of this lack of diversity for what citizen science can achieve remains unexplored. To do this, we reviewed the literature to create a comprehensive list of 70 proposed benefits, outcomes, and impacts of citizen science. We used this list to construct 9 pathways to impact, showing how short-term project outcomes under the themes of data, participant engagement and collaboration lead to a suite of medium- and long-term outcomes. We then explored how a lack of diversity in citizen science participants can cascade through these pathways, affecting the overall ability of citizen science to achieve its myriad potential impacts and further entrenching disparities in society. We advocate for project leaders to use a pathways to impact approach to explore how who they recruit will affect what their projects can achieve. We also call for greater imagination in exploring, testing, and sharing ways in which barriers to participation can be understood and overcome to open citizen science up to all and to achieve its potential.