Swimmers take to the Charles River during the annual City Splash in 2024. (Photo courtesy of Charles River Conservancy)

ALTHOUGH REGULAR SWIMMING in the Charles River largely remains a fond memory from the early 20th century, there is hope.

After decades of unregulated industrialization through the 1970s, the Charles was often too polluted for boating, let alone swimming. But then in 1996, Gov. Bill Weld did something quite eye-popping.

Thirty years ago, he dove, fully clothed, into what was then a very dirty Charles River. Fast forward to today and — due in part to his dive heard round the state moments after signing the Rivers Protection Bill—the river’s health, as measured through the EPA’s “report cards “ has improved from a D in 1995 to the A/B range today.

Through regional collaboration, environmental enforcement, and sustained investment, the Charles has become one of the cleanest urban rivers in the country. But can we keep it that way? Even better, why not set our ambitions high for a river that’s fully swimmable.

Water quality data show the Charles River meets public health standards for swimming on most summer days. And there is real demand to do so.

This Saturday is City Splash, a signature annual public swim and park celebration that provides the public the rare opportunity to swim in the Charles. The event hits swimmer capacity within hours of going live for registration.

The question isn’t whether Charles could support safe swimming. It’s whether we’re willing to make it happen. The Clean Water Act that Congress passed in 1972 promised “to make all US waters fishable and swimmable by 1983.”

In 1995, the EPA announced its goal to make the Lower Charles River swimmable and fishable by Earth Day 2005. Now two-plus decades overdue, the finish line is visible but still stubbornly looms ahead. While we’ve come so far, the extreme weather driven by climate change threatens to erase those gains.

The culprit? Combined sewer overflows, which happen when heavy rain overwhelms sewer systems that carry both stormwater and sewage, causing a mix of runoff and wastewater to be released into public waterways, including the Charles River.

Intentionally designed to release sewage into waterways — and not homes or streets — when the municipal sewage system gets overwhelmed by rainfall, these vestiges of our region’s historical aging stormwater infrastructure are unfit for volatile 21th century weather patterns.

Although much work has gone into upgrading systems upriver, ten active CSOs remain in the urban Charles, which means tens of millions of gallons of sewage-laden stormwater enter the river every year. Despite these facts, tackling CSOs—that is, strategically investing in modern infrastructure to eliminate raw sewage currently being dumped into our waterways— is a hot-button ratepayer issue on full display in the headlines given that the job is not done.

In addition to water quality, another critical component for Boston to become a swimmable city is to design, build, and operationalize urban public swimming infrastructure. We need designated, safe swimming areas with access points, docks, ladders, and floating barriers. We also need real-time water quality monitoring – to track water conditions daily, especially after heavy rainstorms, and clear communications, (similar to coastal beach advisories), to alert the public when it’s safe to swim and build public trust.

And above all we need investment. The Department of Conservation and Recreation has the expertise and maintains more than 450,000 acres and hundreds of unique park facilities throughout Massachusetts, but the agency is facing another major budget cut, further limiting its capacity to keep up with a long backlog of deferred maintenance, let alone spearhead new projects that our communities need and deserve.

We can look at the example of Parisians jumping into history recently. For the first time in more than a century, the Seine River officially reopened for public swimming. The city invested extensively over the past two decades to clean the river and build infrastructure, just in time to debut its facelift for the 2024 Summer Olympics.

What once seemed impossible—swimming in a heavily urbanized waterway—is now an international symbol of what is possible when urban rivers are rightfully treated as public treasures. As for other American cities that have put in the work, we also look to places like Portland, New York City, Chicago, and Baltimore, which are transforming their urban waterways into an open-water swimmer’s dream.

The reason for optimism is clear, but also there’s a need for urgency. The Seine’s transformation didn’t happen overnight. It took conviction, consensus, and leadership to properly invest the time and resources to complete the job.

Boston doesn’t need to replicate Paris’ modus operandi to the letter, but clearly we can see that change can—and should—be done. Committed action from city governments, state agencies, community organizations, and residents can create a clear, collaborative way forward.

Let’s reach the finish line of a swimmable Charles that we set out for ourselves all those years ago.

Laura Jasinski is the executive director of the Charles River Conservancy.