Overall, I really enjoyed reading this paper - well done!

As the paper investigates mainstreaming natural flood managment, the criticism of NFM should also be mentioned within the introduction (e.g. that it would be overwhelmed with extreme floods).

The Ketso method and its applications is well described which makes the method-chapter very transparent. But sometimes it gets lost in details, which makes some texts hard to read. Maybe you can summarise some parts or move them to the appendix.

I would appreciate if you would clearly highlight your most important statements within the conclusions.

First of all, I need to admit that I really enjoyed reading the paper. I positively evaluate the construction of the field research and especially how precisely the work was done and presented. This is not usual for the stakeholder evidence-based papers. I also think that paper is easy to read and that the main findings are highlighted. Also, the paper is well connected to existing NBS/NFM debates and devotes the part for terminological problem.

I missed one aspect that could be added in introductory/review parts before the own methodology is introduced: That is the one of self-engagement of land owners in NBS implementation and how this (rare) self-engagement is viewed (criticized) by FRM experts. Under the pressure of climate change, some land-owners are willing to restore historically changed hydrological conditions of their land, often at their own cost or giving up (agricultural) subsidies for missed production. This engagement shall be cherished and scaling-up potential shall be investigated (as this behavior moves out one of the key barriers – land-owner resistance). But what about coordination problem? I do not insist this debate must be incorporated in the paper, but if authors are open to do so, they might start with: https://link.springer.com/chapter/10.1007/978-3-030-23842-1_6 and follow with responses on this piece: https://link.springer.com/chapter/10.1007/978-3-030-23842-1_7 and https://link.springer.com/chapter/10.1007/978-3-030-23842-1_8.

Overall, I fully support the paper for the publication and congratulate the authors for the great work.

This was a really nice paper to read. It illustrates how to engage different stakeholders in the framing of NFM in the UK through the use of group concept mapping and Ketso methods. The study addresses a very important topic of mainstreaming. It offers practical insights for structuring discussions on mainstreaming issues in NBS and other management and/or domains also. In general, the manuscript is well structured and clearly written. Below are a few comments and questions:

Methods:

The methodological choices can be more explicit in a number of areas (and may be included also in fig. 1). For example:

Section 3.1 describes the participant identification more broadly in terms of the two practitioner groups. What was the criteria for selecting participants from these two groups in each phase? It would help to describe the participants/workshops in section 3.2.1 onwards by referring to the two practitioner groups they belong to. For example, was workshop 1 with flood risk authorities and workshop 2 with catchment partnership members? Also, in some phases the groups are mixed? Were the participants in the three phases the same? The numbers differ over time but were they (a subset of) the same participants from the 1^st phase? Similarly, phase 3 uses snowball sampling techniques to recruit other participants- please explain this design choice and what added value it had in phase 3? I also assume the initial statements generated from both practitioner groups were combined and then qualitatively sorted and ranked separately by the flood risk authorities and catchment partnerships?  Is this correct? If so, please clarify this somewhere in the text also.

Practitioner groups:

Section 3.1.2 (pg 8). Some additional details about the catchment partnerships would be helpful. Is there is a single catchment partnership “network” that exists in the UK with regards to integrated water management or are they specific to different regions/watersheds etc.? This is somewhat unclear from the text. Some examples of the types of actors that are part of these catchment partnerships, aside from the host NGO organization would also be helpful.

Results: I would like the authors to reflect on the following

1. Section 3.1.2 refers to the strategic potential of the catchment partnerships in leading and influencing NFM. At the same time, the authors recognize financial, organizational shortcomings. Does this research reveal new insights on the role of catchment partnerships in mainstreaming NFM?
2. What is the role of the group concept mapping technique in the mainstreaming problem. Is it a useful first step in identifying barriers from different perspectives or, does it also offer insights for exploring how the practitioner groups could identify solutions (based on their own strengths or resources of example) to help overcome some of these barriers?
3. How does this method (group concept mapping) compare to other participatory research methods like for example Q methodology with regards to examining mainstreaming problems?

Overall, I think this paper is a very nice addition to this special issue.