Even though you may not hear about it, hopefully you have gotten someone's attention.

We ride a paved path around a lake here in St. Louis. They have frequent boat races, triathlons, senior olympics that may involve closing part of the path (inconvenient--it's a loop). They always put up signs along the path every intersection, the week before events. It's very considerate and allows us to make alternate plans. I wouldn't be surprised if this didn't develop from a problem way back.

Maybe a follow up letter to all concerned with suggestions for ways to avoid this in the future, such as signs a week before events that would affect the bike path?