In flood protection, the dominant paradigm of ‘building hard structures’ is being challenged by approaches that integrate ecosystem dynamics and are ‘nature-based’. Knowledge development and policy ambitions on greening flood protection (GFP) are rapidly growing, but a deficit remains in actual full-scale implementation. Knowledge is a key barrier for implementation. To analyse conditions for the implementation of GFP, a knowledge-arrangement perspective is developed. The knowledge-arrangement perspective is applied on a case study of successful implementation of GFP in the Netherlands, the pilot Sand Engine Delfland, a large-scale (21.5 Mm3) sand nourishment project. This project confirms that an integrated knowledge arrangement enables GFP as it allows for multifunctionality. Effectiveness of the integrated arrangement in this project is explained by its ‘flexible’ nature providing ample design space. This was possible because core values in flood protection and nature were not part of the integrated arrangement. More generally the case study demonstrates the difficulties of implementing GFP in existing mainstream flood protection routines. These are not (yet) geared to incorporate uncertainty, dynamics and multifunctionality, characteristics associated with GFP. The Sand Engine project can be regarded as a ‘field laboratory’ of physical and institutional learning and an innovation for mainstream flood protection.