(AP) - Water quality in the Potomac was already bad and has grown worse in the past five years, as the river responsible for much of the District of Columbia's drinking water faces upstream pressures from forest loss and farming and downstream stress from growing development, the Potomac Conservancy said Thursday.
In its annual State of the Nation's River report, the conservancy gave the waterway a D grade, down from D+ in its first report in 2007.
The conservancy says there are new concerns as well, including contaminants such as chemicals found in the river that have been linked to so-called intersex fish that have both male and female traits.
"The nation's river continues to face significant threats," said H. Hedrick Belin, president of the Potomac Conservancy.
More than 6 million people now live in the river's basin in Virginia, Maryland, West Virginia, and Pennsylvania, up 5 percent in the past five years.
The river's vital signs have leveled off or declined as a result, the conservancy said, noting that in 2010 the river had the second largest decline in scores compiled by Chesapeake EcoCheck, a government university partnership, with four of six major health indicators declining.
The river, for example, is often unsafe for swimming after heavy rains because many sewage systems are tied to storm drains that overflow, a problem that only increases with the population, the conservancy said.
About half of the river basin is still forested, but development in downstream areas is depleting woodlands, with Prince George's County losing about half of its forests between 1993 and 2007. And upstream, where forests increased over the past century as farm lands were abandoned, that trend is being reversed due to growing development, the conservancy said.
That's important because forested acres produce 95 percent less runoff during storms than paved areas of the same size. While many of the farms that remain are well managed, larger animal feeding operations are an increasing threat because of the amounts of manure the animals produce, Belin said.
Runoff from manure and fertilizer from croplands, lawns and other sources harms water quality by promoting the growth of algae, which clouds water and robs oxygen once the algae dies and is broken down. That can lead to dead zones where the water lacks enough oxygen to support plants, fish and other organisms.
The conservancy said progress has been made in the past five years, but not enough to get ahead of the growing problems.
Many recommendations involve limiting runoff from developed areas.
Forests also must be protected through conservation of existing areas and replanting, particularly along stream banks with a goal of a no-net loss of forests. The group is also calling for tighter toxic chemical controls.
Todd Lookingbill, an assistant professor of geography and the environment at the University of Richmond, said the effect of development on streams and small waterways is often overlooked.
Small waterways, which sometimes do not have water year-round, are "hot spots of biological activity"' that help remove pollutants, but they are often turned into culverts, channelized, or paved over.
"By not allowing the water to interact with the land we are reducing the ability of the natural environment to filter these contaminants," Lookingbill said during a conference call.
Lookingbill said development was also increasing in what he called "exurban" areas which are often rural.
Developers, meanwhile, are often hampered by regulations that limit what can be done to reduce runoff, Belin said.
Some communities, for example, require streets to be 30 feet wide when narrower streets would limit the amount of paved area. Developments in some places are also required to have a certain number of parking spaces, or don't allow more porous paving materials, he said.
Local governments, he said, "need to step up in the coming months and lay out their plans for how they are going to reduce pollution in their communities." He said it will pay "tremendous dividends down the road in terms of clean and safe drinking water."
Controlling runoff is a key feature of the federal Environmental Protection Agency's strategy for restoring the Chesapeake Bay, which the Potomac feeds, Belin noted.
While gains have been made in cutting pollution from farms and sewage treatment plants, the EPA says pollution from urban and suburban runoff is still growing.
The Potomac Conservancy has not graded the waterway since the first report in 2007. Conservancy spokeswoman Anne Sundermann said the new grade is part of its plan to reassess the waterway every five years.
Jenn Aiosa, a senior scientist at the Chesapeake Bay Foundation, said the report isn't surprising, noting continued population growth.
"I think the Potomac is, unfortunately, the perfect poster child for how we are changing the landscape," Aiosa said.
While bay restoration efforts sometimes suffer from a disconnect between those who live far from the Chesapeake and don't see the link to their local waterways, Aiosa said the report could be a wake-up call for residents to demand clean drinking water.
"There are a whole bevy of emerging contaminants that we have no idea what they mean for human health and they are out there in our drinking water," Aiosa said.
The challenges facing the river as it travels from its rural headwaters, past Washington and into the Chesapeake show that keeping the district's drinking water clean, and ultimately the bay, requires the problem to be addressed on multiple fronts, she said.
"We can't necessarily look for the silver bullet," Aiosa said. "We have to address wastewater treatment, the septic systems, the farms, the sprawl development, the roadways, everything."