As we rounded a bend in the Charles River last Sunday, almost keeping pace with runners trotting along a shoreline path, I took my eyes off a digital timer on the kayak deck to glance at the Boston skyline that rose above the trees.

“Should be hitting the turn-around pretty soon!” I called ahead to Phil Sachs, who was paddling in the bow of his 22-foot tandem vessel while I flailed away in the stern.

“Just past the B.U. Bridge,” he replied, not missing a stroke.

Years ago, I wouldn’t have been too eager to paddle on a river so filthy that it gained notoriety in a popular song.

“Dirty Water,” a 1966 hit by The Standells, includes these memorable lyrics:

“Yeah, down by the river

Down by the banks of the river Charles …

Well, I love that dirty water

Oh, Boston you're my home”

Happily, since “Dirty Water” first hit the airwaves, the 80-mile river that flows from Hopkinton to Boston has cleaned up its act considerably. Improvements can be attributed to federal anti-pollution laws and the efforts of a growing environmental movement made up of organizations such as the Charles River Watershed Association, which sponsored last week’s competition.

Under cloudy skies, scores of kayaks, surfskis, canoes and standup paddle boards churned along in a series of races of various distances. Phil and I entered the 6-mile race, and I’d like to brag about easily winning our division, but in truth, it was a tiny division.

Immediately following a chaotic mass start, another pair in an identical tandem kayak bumped our stern while trying to draft off our boat, which was all it took for Phil to crank up a fast cadence.

After a few minutes of furious paddling, we pulled away and never looked back.

Meanwhile, I could see my son, Tom, paddling ahead with Phil Warner in a longer, sleeker tandem, blasting through the water like a torpedo. Fortunately for Phil Sachs and me, they were in a different division — and also won. That’s long been a key to my kayak-racing success: paddling in a limited division.

For the most part, though, competition among paddlers has been spirited, not cutthroat. The real reward Sunday wasn’t a trophy but the gratification of supporting a worthwhile conservation organization.

Formed in 1965, the watershed association has helped organize cleanup campaigns, backed anti-pollution legislation, lobbied to stop new dam construction and encouraged preservation of 8,000 acres of surrounding wetlands.

Today, the Charles, like many urban rivers once valued primarily for transportation and hydroelectric power, is treasured as a natural and recreational resource.

In pre-Colonial times, Native Americans exclusively canoed and fished the river, and when European settlers arrived in the early 17th century, they began building mills and dams.

These dams, which now number 20, initially were beneficial — not just by providing power but also, in the case of the Moody Street Dam, by creating a 200-acre mill pond along with scenic bays and inlets between Newton Lower Falls and Waltham that became a major tourist attraction at the turn of the 20th century.

At the same time, though, other parts of the river deteriorated. An 1875 government report noted that waste discharged by mills and homes along the river — the most heavily populated watershed in New England — had all but eliminated native fish populations. Authorities declared the river so foul that there was not much point in trying to clean up the lower half from south Natick to Boston Harbor.

Luckily, that idea was abandoned, and remediation plans began.

A dam built in 1910 where the Museum of Science stands today included ladders that allow migratory fish to proliferate. Today, some 20 species swim in the Charles.

This dam also created the Charles River Basin, a waterfront park now home to one of the world's largest public sailing programs, as well as several yacht and rowing clubs. The basin also is the site of a world-class rowing regatta, the Head of the Charles (not to be confused with the Run of the Charles paddlng races we competed in last Sunday).

As for the infamous song, though the lyrics may no longer apply, “Dirty Water” lives on.

In 1997, the Boston Red Sox declared it the team’s "official victory anthem," to be played after every home triumph. The Standells even performed “Dirty Water” before the second game of the 2004 World Series at Fenway Park.

The Sox then shut out the St. Louis Cardinals, 4-0, and went on to sweep the series for their first championship since 1918, so I guess the legacy of “Dirty Water” proved to be a win-win for Boston after all.