With an apologetic shrug, Hedrick Belin lifted the battered horn to his lips and gave a mighty blow.

In former times, a canal boat captain would have used the same horn to call the lock keeper to let his boat pass. But on this Sunday morning, the raucous note merely drew a glance from marathoners on the towpath. Up in the trees, the warblers kept warbling and the titmice continued their twittering.  

Belen is president of the Potomac Conservancy, and he and a group of well-wishers were on hand to officially open the River Center at Lock 8. Want to learn more about the river? Help protect it? Need an excuse to get wet and muddy? This is a good place to start.  

The conservancy’s outreach activities have already been going full swing, said Belin. So far this year, the number of volunteers participating in conservancy events equals last year’s total.

The volunteers clean up trash, plant trees, serve as docents at the River Center, and do administrative work for the conservancy. They also care for two miles of shoreline upstream and down from the Lock 8.

Upcoming events include a wildflower walk, a monthly cleanup, towpath restoration and a tutorial on medicinal plants.

 “One of our main aims is getting people out,” Belin later told me. “We want to help people connect with this wonderful resource.”

We had already connected that morning on a bird watching jaunt led by sharp-eyed birder Paul Hagen. The morning’s highlight, at least for me, was a great-crested flycatcher, barely visible on a snag on a little island.  

The birds use tree cavities for their nests, which they often line with shed snake skins. Some believe they do this to discourage predators. Or maybe the birds just like the crinkly texture, since another favorite nest building material is cellophane food wrappers.

The morning ended on a rocky note with Callan Bentley, geology professor at Northern Virginia Community College.

With the flair of an impresario, he held aloft a ball of imaginary pizza dough, which he proceeded to stretch, and then tear. This was what happens to the earth's continental crust when oceans are formed. If the crustal “dough” had torn apart a little further west in the last ocean building episode, he said, Potomac, Md., today would be on the west coast of Africa.

Yes, geology does take a long time, but it’s also happening now. Sometimes you can even hear it happening, such as when the floodwaters from Hurricane Isabel set boulders rolling and scraping down Mather Gorge. Keep it up long enough, and those boulders will become mere rounded pebbles.  

How long does it take to make a rock? “Pick up some mud and squeeze it hard,” Bentley said. “What you get is low-grade lithification,” basically a really soft rock.

He led the group to some rocks washed down the hillside. He picked up a dark specimen. Once, he said, it was buried deep below an ancient ocean. He picked up another piece, even darker. “Urbanite,” he said. It was a chunk of asphalt, probably from the parking lot up the hill.

When it’s not engaging the general public, the conservancy works to beef up local environmental policies. Partly as a result of its efforts, Montgomery County now requires that highway designs include natural water filters, such as grassy medians and tree plantings, for reducing polluted road runoff into local streams.

Protecting nature’s own filtering systems is another conservancy goal. The group’s staff works with landowners to enroll in state-managed programs to safeguard forests, pastures, and particularly buffer zones along streams. With its help, some 12,000 acres of land received formal protection over the past decade.

Another big issue is the health of the river itself. Scientists have concluded that some of the cocktail of man-made chemicals that eventually enter the river effectively lower the disease resistance of fish, resulting in lesions and fish kills. Some of these chemicals, called endocrine disrupting compounds, are suspected of causing the widely publicized intersex fish, in which males develop ovaries. The conservancy will provide an opportunity for the public to learn more about these issues at a forum on June 3.

Other conservancy campaigns address problems that are just too glaring to ignore. Belin is particularly galled by the Trump National Golf Course’s razing of hundreds of trees that formerly protected the riverbank across from Riley’s Lock.

But the golf course’s environmental manager has a different view on the effect of trees on erosion control. He said that the aim of the deforestation was to “stabilize the shoreline.”

Of course, the real reason Trump National cut down the trees was to give golfers a better view of the river as they ride about on their carts.

“You would think that they would just want a view here and a view there,” said Belin. “It turned out that they wanted it all.”

In the face of relatively lax Loudoun County regulations, he’s counting on public pressure to get the Trump operation to repair the damage.

This is what it takes: people who know the river, love being with it and who are determined to protect it.