Please be respectful of other park patrons and wildlife.
Dogs in public places are like kids: Not everyone wants them around, and even those who like them may be somewhat annoyed by disruptive behavior.
People watching wildlife will not be too happy if your barking dog scares the critters away, and someone floating on a lake might not want to be joined by your wet, hairy friend.
Carry plenty of water for everyone (not all sources of water are safe for your dog to drink) and snacks for your dog if you will be hiking or otherwise active.