Amid all the 50th anniversary observances that recall the pain of 1968, one marked by a new documentary is more uplifting. Fifty years ago — thanks in part to the leadership of two Minnesotans — federal legislation was enacted that has been key to shielding the St. Croix River and its Namekagon tributary in Wisconsin from development.

That story is told in "The Wild and Scenic St. Croix," a film that will have its debut Sunday at 7 p.m. on TPT's Minnesota channel. It's the handiwork of Afton Films, a production company headed by someone who knows the power of public policy, legislative staffer-cum-lobbyist John Kaul. His partners in the project include co-producer Tom Reiter, renowned nature photographer Craig Blacklock and the St. Croix River Association, the nonprofit ally of the St. Croix National Scenic Riverway.

The film tells how three determined Midwestern lawmakers — Wisconsin Sen. Gaylord Nelson and Minnesotans Sen. Walter Mondale and Rep. Joe Karth — collaborated to enact the National Wild and Scenic Rivers Act. The 1968 legislation specified eight rivers for its initial restrictions on encroaching development. One of the eight was the St. Croix, which Nelson said was at risk of becoming "a floating Coney Island" as the Twin Cities area grew unless the federal government acted.

It was then-Northern States Power Company's construction of a large coal-fired power plant near Stillwater in the 1960s that spurred Congress to act. By the time it did, NSP had dropped earlier plans for hydro-power generation on the river and joined the cause, donating 25,000 acres of land to create the riverway."

This is a success story to date. But the story isn't over. New threats to the river are coming from climate change, invasive species, and runoff from lawns and fields far from the river's edge. Keeping the river healthy for the next 50 years and beyond will require concerted action from more people in more places than the 1968 act contemplated.

"We won't lose [the river] through some big dramatic destruction ... but we could lose through what I call nicks and cuts," Mondale warns in the film. "Before you know it, if we're not careful, the river as we know it will be gone." Mondale did his part 50 years ago to prevent that. This anniversary observance should inspire a new generation to take up the cause.