I was just out there this weekend working with scouts on the trails. I can't speak for all the trails, but some would be difficult to navigate in a wheelchair and maybe scooter. They can be narrow and uneven in spots. But there are car lanes in some areas where you maybe able access with permission. I would call and see. The boardwalks do have some boards missing/broken on some trails as well.
I would say that all of it is accessible. There are boardwalks and grass paths. No stairs in my memories, all ramps.
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