ERROL, N.H. – Canoeists and kayakers will be out on the Androscoggin River in New Hampshire and Maine for what has become a rolling series of day trips promoting awareness and fostering stewardship of the 167-mile river.

Paddlers began the day Tuesday at the outlet of Lake Umbagog near Errol and will complete the journey July 25 at Maine’s Fort Popham.

It was in 1995 that Marcel Polak of Woodstock, Maine, helped organize what’s become the annual Androscoggin River Source to the Sea Canoe Trek. Polak sought to highlight the importance of a river once ranked among the nation’s most polluted.

That first trek attracted 10 to 12 people some days and only a handful on others. But over the years, thousands have been taking part.

“We didn’t know what we were getting ourselves into, because we didn’t know the river well enough,” Polak said.

In 1999, the fourth annual trek spawned the Androscoggin River Watershed Council, which now coordinates the event and labors to protect the watershed.

“To our knowledge, it is the only source-to-the-sea river journey in the United States that is held annually,” said council trek coordinator Barbra Barret.

Before cleansing of the river began, the Androscoggin River was full of industrial sludge.

John M. Kauffmann’s 1973 book, “Flow East: A Look at Our North Atlantic Rivers,” describes a trip down the river “on a torrent of foul and sulfurous soup. … Instinctively, we tried to dodge the foam that formed a thick scum upon the water and the sludge that floated by like dinosaur stools.

“Instinctively, too, we raised our nostrils to try to catch what breeze of sweet air might blow down from the mountains to dispel the river’s fetid breath that rose from its mire in nauseating bubbles.”

Kauffmann blamed three paper companies for contributing more than 90 percent of the pollution in the Androscoggin, and for its near destruction. Municipalities, businesses and people piped raw sewage directly into the river as well.

The Clean Water Act, however, made it illegal to discharge pollution into the nation’s waterways without a permit.

It also forced paper companies, municipalities and industries to build wastewater treatment plants to meet technology-based, water-pollution-control standards.

By the time the trek began, the river had improved vastly. It didn’t smell as much, Polak said, and wildlife was rebounding.

The biggest threat now, Polak said, is the greater interest in waterfront property.

“Ten years ago, it was not an area that people considered as having value. There was no market for Androscoggin River frontage, but slowly, as we started the trek, that shifted things,” Polak said.

What once was valuable farmland along the river is being sold at an alarming rate to developers, Polak said.

“I’m seeing more and more houses now along the river, despite shore land zoning laws. Now, what I’m concerned about is the suburbanization of the river,” he said.