The Baltic Data Flows project, co-financed by the Connecting Europe Facility of the European Union, seeks to enhance the sharing and harmonisation of data on marine environment originating from existing sea monitoring programmes, and to move towards service-based data sharing. In particular, open datasets will be made available by the Baltic Marine Environment Protection Commission (HELCOM) to a wider community, such as European open data ecosystem, researchers, NGOs and private sector, in order to benefit from the availability of harmonised environmental data. More specifically, Baltic Data Flows will: (1) Increase capacity for national competent authorities for harmonising and sharing collected environmental monitoring data on the Baltic Sea by supporting development of database platforms; (2) Further develop and implement a system for harvesting environmental datasets from national sources to regionally harmonised datasets by extending the piloted harvested system developed between the project partners ICES and SMHI; (3) Provide support to regional harmonisation and create data products supporting environmental assessments by further defining the data needs and existing reporting formats; (4) Make harmonised datasets accessible and discoverable in the European Data Portal (EDP) by using DCAT-AP compliant metadata catalogues. Baltic Data Flows will improve the capacity building of the national environmental data hosting organisations and providers of the consortium, in terms of quality control and solutions to make harmonised environmental data available.