Accessing rivers and streams is a “fundamental component of our culture and identity,” says an unnamed narrator in the opening minutes of a Colorado filmmaker’s latest short film. Yet it is also “an enduring conflict.”  In his 20-minute documentary “Common Waters,” filmmaker Cody Perry puts a spotlight on Colorado’s murky river-access laws and how decades of ambiguity have led to public confusion. … The issue has a long and tumultuous history in Colorado, which has seen a host of legal battles over recreationists entering sections of waterways that overlap with private land. At the center of the debate is the question of when and whether the public has a right to use those segments of streams.