Potomac — The Potomac River is struggling, according to the Potomac Conservancy’s State of Nation’s River.

The Conservancy cites the challenge of protecting the river in a variety of settings in its annual report, which lowered the letter grade given to the health of the river late last year to a "D." Since 2007, the grade has been "D+."

More than 6 million people live in the Potomac River Basin, and another 600,000 people could move to the region in the next decade.

As population rises, so does the amount of impervious surface. Streams begin to degrade once 10 percent of a watershed is paved, according to the Potomac Conservancy.

The Potomac River flows through a variety of habitats and environments, starting in forests, traveling through farmland and then through areas that are growing rapidly. While Montgomery County has done many things to protect the river and water quality, population growth has brought new development and more paved surfaces. Even though much of this new development is not near the river, it has an effect because of the contaminated runoff that flows into the river every time it rains.

"Rapid development has caused many small headwater streams to become ‘buried’ — paved over or rechanneled into culverts and storm drains," according to the report. Stream burial "dramatically" degrades stream health and water quality.

THE LAND around the river in Montgomery County has long been defined as a "green wedge," with larger lot zoning and more protection for the forests along the river. This is one of the major reasons the local area has its semi-rural character.

Montgomery County is in the midst of completely rewriting its zoning code, and the health of the river is one reason this effort matters. Density, stormwater runoff, stream and streamvalley quality and impervious surfaces even on the other side of the county from the river, all make a difference in the quality of the drinking water that comes from the Potomac.

See www.montgomeryplanningboard.org/development/zoning.

Another challenge from increasing population is a relatively new contaminant class, at least some of which comes from pharmaceuticals. The reports says that scientists have found hundreds of "endocrine-disrupting chemicals" in the river. Effluent from wastewater treatment plants and runoff from farms are likely contributors to this contamination that has caused "intersex fish."

Volunteers Sought for River Cleanup

MONTHLY CLEANUPS continue at The Potomac Conservancy’s River Center on Sunday, Feb. 5, from 10 a.m. to noon at Lock 8.

The River Center is a cooperative project of the Potomac Conservancy and the National Park Service.

See www.Potomac.org.

Volunteers are also needed for the Alice Ferguson Foundation 25th Annual Potomac River Watershed Cleanup on April 14.

In 2011, 11,388 volunteers removed 228 tons of trash, including 20.66 tons of tires and 14,606 bags of trash and recyclables from 613 sites along the Potomac River watershed, according to the Alice Ferguson Foundation;

15.1 tons of recyclable materials were actually recycled after last year’s cleanup.

Sites for the April cleanup include Angler’s Inn, Carderock Park, Great Falls Tavern, Pennyfield, Riley’s, Violette’s and Swain’s locks

See www.fergusonfoundation.org.