Public participation in science is burgeoning, yet little is known about factors that influence potential volunteers. We present results from a national survey of 1,145 marine users to uncover the drivers and barriers to a sightings-based, digital marine citizen science project. Knowledge of marine species is the most significant barrier and driver for participation. Many marine users perceive that they have insufficient knowledge of marine species to contribute to the project, yet they expect to learn more about marine species if they were to participate. Contributing to scientific knowledge is also a strong driver for many marine users to participate.