Citizen science is becoming a key tool for monitoring marine biodiversity. By involving people in observing and recording species, we can collect valuable data across wide areas and over long periods of time — something that would be hard to do with traditional scientific methods alone. At the same time, these initiatives help raise awareness and connect the public with marine conservation. One of the main challenges, however, is ensuring the quality and consistency of the data collected. That’s why well-structured projects that combine public participation with scientific validation are so important. The BioMARatona is a national-scale citizen science initiative developed under the European project ANERIS, with the goal of promoting marine and coastal biodiversity monitoring across continental Portugal. Inspired by the Bioblitz model but extended over several months (May to October), the BioMARatona encourages participants to document biodiversity using the MINKA platform, where observations are later verified by experts. The BioMARathons concept originated in Barcelona in 2021 and was implemented for the first time in Portugal in 2024. That first edition resulted in over 1,000 biodiversity observations, the registration of more than 170 species, and contributions from over 100 volunteers. In 2025, the initiative returns with an expanded scope, engaging more schools, municipalities, and local communities. This presentation will share the evolution, structure, and preliminary results of the BioMARatonas, highlighting the potential of citizen science to contribute meaningfully to biodiversity research and long-term marine monitoring efforts in Portugal.