The city I live in sits on the confluence of the Tuolumne river and Dry Creek.
Back in the early and mid 70's a bunch of kids, including myself, built a network of trails to ride on.
The city tried to close what we built, to us, for bird watchers. For some of the kids in this area it's the only thing they can do that doesn't cost stupid money. They quickly gave up trying to enforce it. Critical mass type events work.
That's because a bunch of old men, the same guys who worked down here were willing to show up.