It may be that the current board has the right to block the road to non-members as you say "to the HOA.permited fishing dock and launch ramp." They may have obtained permission on the grounds that only HOA members use the dock and launch ramp.
Now if the TVA had a launch ramp and fishing dock by using the same road I don't believe the HOA could block it.
Probably trying to force the non members to join!!!!
Just my 2cents.