LAST SUMMER, plunging through the major rapids of Manchester, I found myself doing something I’ve counseled many others not to do — kayaking on the Merrimack. Just a day after a major rainstorm, my party of seven put in at the Amoskeag Dam and paddled south.

What a day it was: radiant in early summer gold. Down below, the river looked spotless, too — certainly compared to its state in the 1960s. Then, it was considered one of the 10 filthiest waterways in the country. We’ve rowed a long way since.

How did we do it? Partly it was due to local residents’ growing belief that no one should have to put up with smelly rivers. Dirty water taxes public health and wildlife in myriad ways. And partly, it was due to a powerful statute, the Clean Water Act, which in 1972 was fashioned into its modern shape by representatives and senators so committed to a clean environment that they delayed their planned recess to inundate President Nixon’s veto by huge majorities: 247-23 and 52-12.

Crucially, the Clean Water Act pumped more than a hundred billion dollars into modernizing the nation’s wastewater treatment systems — including Manchester’s sewage plant, opened in 1975. Before that, human and industrial waste gushed directly into the Merrimack. In fact, Congress expected America’s waterways to be fishable and swimmable by 1983, with all discharges halted two years later.

That didn’t happen, and a major reason it didn’t was because the law had some very large holes in it. One of the biggest was visible on our kayaking journey, where we navigated the cascading whitewater three times before arriving at Reeds Ferry in Merrimack.

Although the rapids had their way with a few of us, fortunately we were upright and dry when, a few miles above our planned take-out, we came upon an expanse of curious whirlpools in the center of the river. Upon inspection, each turned out to be tiny vortex of sewage, drifting lazily alongside our small, colorful armada. How they got there was not hard to figure out: the most likely source was the Merrimack River’s biggest polluter — the city of Manchester’s sewage treatment system.

Last year that system dumped a mixture of more than 360 million gallons of raw sewage and polluted rainwater into the river — a record for the past six years, the only period for which the city appears to have kept data.

Known as a combined sewer overflow (CSO), this phenomenon happens when a sudden or persistent rain overwhelms the collection system, forcing it to discharge untreated waste into the river. In 2018, Manchester’s overflows accounted for nearly half of the 770 million gallons of CSO sewage dumped into the Merrimack. That’s a big reason that the river still doesn’t meet Clean Water Act standards.

It also makes things less easy for the 600,000 people who live below the Queen City and who depend on the Merrimack for their drinking water. (In fact, the river is New England’s second-largest source.) What’s more, as a general rule, the sorts of bacteria that thrive in sewage — coliform — can stay active for up to three days. As many already know, E. coli and friends cause major intestinal distress. They present particular risk to the very young, the very old, and those with compromised immune systems.

So it’s really too bad that the Merrimack not only will remain impaired for many years (it takes time and money to address the CSO problem), but also that, in the meantime, we know so little about what the river’s biggest polluter is up to.

Right now, if you were interested in knowing how much sewage the plant is dumping into the water, you’d have to wait until mid-January of the following year. And even then, the total is hard to come by. I had to call a contact at the state Department of Environmental Services to find out.

Does Manchester’s wastewater plant disclose how much sewage it dumps from its 15 CSO outlets during any given rainstorm? No.

Does the city afford kayakers, anglers, jet-skiiers, waders, and people walking water-loving dogs real-time notice that it is inflicting a sewage overflow upon the river and where along its five-mile stretch of CSOs this is happening? No, it doesn’t.

In fact, it doesn’t provide the public with notice at all.

For us kayakers, the Merrimack looked inviting that morning, especially in the bright summer sunlight after a few days of rain. But, looking back, you have to ask, What’s wrong with this lovely picture?

Robert H. (Rusty) Russell is Executive Director of the Merrimack River Watershed Council.