River restoration has grown from something of a fringe movement to become a global phenomenon attracting adherents from around the world. How does it feel to see people respond so positively to this movement now?

I am really proud, as is all the team at the World Fish Migration Foundation. It is so inspiring to see so many organisations around the world using World Fish Migration Day as momentum to raise awareness, or to celebrate the removal of a dam or inauguration of a fish passage facility. Knowing that people take schoolchildren out into the field for activities under the umbrella of World Fish Migration Day is something that makes me really feel proud and motivated to step up another level and keep moving forwards. Because I think we haven't reached our potential yet; I think at this point in 2018 we had 570 all around the world, from New Zealand to Hawaii, in 63 countries. But I think, knowing what is out there and knowing how many people we haven’t reached out to yet, that we could easily go over 1000 events—and maybe 2000 is even possible.

It's a potential we haven't reached yet, but we’re trying.

For example, last week I went to the offices of Trout Unlimited. Trout Unlimited has a network of over 200 regional local groups.

If they become inspired to help out as well, just imagine how many organisations will be involved next time. Networking and getting more organisations on board is quite hard to manage, by the way; every time we step this up we have more people to connect to and prefer to keep it personal and stay involved. So we definitely need help from other organisations to get our messages across. It's a tough job to be in such a big network.

I can only imagine. If there was one thing that you would like people to take away from watching this film, what would it be?

That it's possible to restore rivers again and to get migratory fish that were in these rivers back again. That it’s possible to get a river that really is alive and actually provides fish, in some cases providing food, but also maybe providing an economy like fly fishing - a completely different way of looking at rivers. And I'm not saying that I want to remove all hydropower dams around the world. I just want to say that it's possible to remove old and obsolete dams from rivers and to balance the river management a little bit better than we used to. So that for example, you decide that some rivers are kept free flowing and that some are for hydropower use. But at this moment, there are so many hydropower plants appearing everywhere that my take home message would be, "protect what's still free-flowing and open up and restore where possible".

And that's a wonderful philosophy to have.

The simple message is that it is possible to open up rivers by removing dams. I started my work by building fishways in the past, but ended up leaving that topic to an extent because actually, I think that it's much smarter and easier to remove dams - the river comes back to life. It works out much cheaper because you don't have to build and maintain a fishway, you don't have to maintain an old dam - it's much, much easier from a cost perspective.

It's a serious topic and what we do is take a serious topic and make it a little more attractive for the general public, so that people start to understand what's going on. The title of our documentary, Love Flows, and our symbol of the Happy Fish, were chosen to make our message more accessible for people out there.