This document discusses lessons learned from the #adoptaunaplaya project, which gathered environmental data about beaches in Spain from various open data sources. It summarizes the data sources used, including PRTR reports on water waste and bathing water quality. Some difficulties encountered were that the data was not always updated and there was a lack of data harmonization between national and European schemas. The document also discusses challenges of working with open data and big data, such as ensuring data is structured, in open formats, and linked to other sources to maximize its value.