IDEATION (InlanD watErs in the digitAl Twin OceaN) aims to prepare the development of the digital twin of the inland waters (rivers, lakes, reservoirs, wetlands, snow, and ice) addressing activities to be developed and to make it integrated and interoperable with the DTO for a unified digital twin of ocean and waters (addressing the hydrosphere as a whole). IDEATION will be based on a cross-border cooperation, involvement, and commitment of stakeholders at European level by following the Water-oriented Living Labs (WoLLs) approach. Stakeholders will be engaged via Multi-Stakeholder Forums (MSF), using a range of different engagement methodologies (e.g., focus groups, workshops, interviews, questionnaires) depending on goals of the engagement and specificities of the context. A comprehensive review will be performed to make an open knowledge inventory for inland water systems (OpenKIWAS). IDEATION will co-design the IDEATION reference architecture defining a set of building blocks, interfaces and standards to make data, models and technologies interoperable and integrable with the DTO. Putting together all the results from the MSF, OpenKIWAS, and the IDEATION reference architecture, a roadmap for the integration of inland waters in the Digital Twin Ocean will be created providing a preliminary breakdown of the work, with priorities of implementation, into a stepped approach. The consortium members have high experience on EU project coordination and participation, the majority of them already worked together in research projects.