Cattle and algae Shenandoah River

Cattle stand on the banks of the North Fork of the Shenandoah River in Rockingham County, VA, where a harmful algal bloom recently closed more than 52.5 miles of the waterway to recreational uses. (Alan Lehman/Shenandoah Riverkeeper)

Carpets of grass-colored algae have long plagued the Shenandoah River in Virginia, making it unpleasant to be on the water during some of the hottest weeks of the year. And, the problem is getting worse. This summer, the state declared that an expansive algal bloom impacting more 52.5 miles of the river’s North Fork was not only unsightly and foul-smelling but also toxic to humans, pets and wildlife.

The public health advisory was lifted in mid-September, nearly eight weeks after it was issued.

For Shenandoah advocates, the blooms — both those that are a nuisance and those that could harm users of the river — are a glaring reminder that more work is needed to clean up agricultural pollution in the region.

Algal blooms occur in the Chesapeake Bay, as well as streams, rivers and lakes throughout the Bay region. They generally indicate an ecosystem out of balance. Some factors fuel them, particularly in slow-flowing or shallow waterways. Among the culprits: Nutrient pollution from fertilizers and sewage, as well as increasing problems from climate change, such as extreme wet and dry spells and warmer water temperatures.

In the Shenandoah River basin, drought conditions this summer set the stage for a bloom that began to grow in July. Since mid-June, the North Fork of the Shenandoah — already a shallow waterway compared with others of its size — was below its 96-year average depth, according to a river gauge at Strasburg.

Shenandoah Riverkeeper Mark Frondorf said this year’s crop of algae was a particularly bad version of the ones he’d seen in previous years and reported it to state authorities. Frondorf and the Potomac Riverkeeper Network have submitted dozens of complaints about algae blooms on the Shenandoah over the past decade.

Harmful Algal Bloom Shenandoah

An algal mat hugs the surface of the North Fork of the Shendandoah River near Lower River Road in Tom’s Brook, VA, on July 28. (Linda Allen/Courtesy of Friends of the North Fork)

“On the North Fork, you get these big thick algal blankets, and they smell,” Frondorf said of the bloom that developed in July and August. “A lot of people think there’s been a sewer pipe that’s ruptured. It’s such an awful, foul smell.”

The Virginia Department of Health regularly tests along certain public saltwater beaches for the presence of harmful algae blooms as well as bacteria that make swimming unsafe. But testing in freshwater rivers is inconsistent and typically in response to a complaint.

After finding cyanobacteria in the Shenandoah’s algae in mid-July, the county and then state health authorities issued advisories warning people to avoid the river. This less common type of blue-green algae releases toxins that, when touched or ingested, can cause rashes and gastrointestinal illness, and it can be fatal to dogs and other animals.

Additional testing in early August caused the state Department of Health to expand its advisory to encompass a total of 52.5 miles of the Shenandoah’s North Fork, a winding but shallow section of the river that laces through the state’s Seven Bends State Park in Woodstock.

Blooming numbers

Harmful algal blooms aren’t new. But the problem has spread as freshwater blooms increased significantly over the past 40 years, making them an environmental problem in all 50 states. In the Bay region, a 2015 study found that harmful blooms were occurring more frequently than they had 20 years before. Blooms across the country have been the subject of nearly 400 news reports so far this year, according to the nonprofit Environmental Working Group, which has tracked a rise in such reports over the last decade.

In late August, harmful algae blooms were also proliferating across Hampton Roads near the Chesapeake Bay Bridge Tunnel in Virginia. Aerial photos taken by the Chesapeake Bay Foundation after an open-water swimmer reported them showed reddish-brown blooms streaking waters near the mouth of the Bay and in the Lafayette and York rivers.

Bay Bridge Algal Bloom

A harmful reddish-brown algae bloom appeared near the Chesapeake Bay Bridge Tunnel on Aug. 26. (Chesapeake Bay Foundation and American Multimedia Solutions)

In Maryland, the Frederick County Health Department told residents to stay out of the water at Cunningham Falls State Park just before Labor Day weekend due to toxic algae blooms.

Though this summer was the first time a section of the Shenandoah River was under a recreation advisory for a bloom of cyanobacteria, the river has a long history of being burdened by other types of algae.

The Shenandoah Riverkeeper and Potomac Riverkeeper Network sued the U.S. Environmental Protection Agency in 2017 over excessive algae, which had caused fish kills and was regularly rendering the river unusable. They asked the courts to compel the EPA and Virginian to declare the Shenandoah River impaired by nuisance filamentous algae.

Inclusion on the state’s impaired waters list would allow the Virginia Department of Environmental Quality to develop specific plans to reduce pollution from the surrounding landscape, much of it farmland. The courts, though, ruled that the DEQ left the river off the list for good reason, pointing out that Virginia did not have a water quality standard for algae that could trigger such a listing. The decision stood despite an appeal that wrapped up in 2020.

Since then, the DEQ has been working on the issue anyway, under pressure from environmental groups that have been tracking algal blooms on the Shenandoah for more than a decade. The agency determined that it could develop a standard for measuring algae that would, over the course of a few years, help to determine whether a waterway is impaired by the amount of algae occurring.

This would be similar to a chlorophyll a standard that was developed for the James River a few years ago. The James is currently the only Bay tributary with a specific numerical limit for chlorophyll aimed at reducing algae.

Measuring chlorophyll in water is a surrogate for directly measuring algae biomass, a process that is far more expensive and time consuming. Chlorophyll is the pigment that allows plants, including algae, to convert sunlight into compounds through photosynthesis. Chlorophyll a is the predominant type in algae.

DEQ spokeswoman Ann Regn said the criteria being considered would help protect recreational users in portions of the Shenandoah River’s North Fork, South Fork and mainstem from nuisance filamentous green algae.

The agency does not at this time plan to adopt criteria to address blooms caused by cyanobacteria, like the one that occurred this summer.

“Filamentous green algae have been the focus of concern in the Shenandoah in recent years because large occurrences of cyanobacteria [in] mats or in the water column have not previously been observed by DEQ,” Regn wrote in an email. 

Contributing factors

Runoff from agriculture operations often contains nitrogen and phosphorus — nutrients derived from manure and fertilizer — which are the primary cause of algae blooms and other water quality woes in the Bay and many of its rivers.

Advocates have long pegged runoff from livestock and poultry operations as a major contributor to the overgrowth of algae in the Shenandoah River. Cattle that have access to the river can defecate in it. And manure from large poultry operations, which is often spread on nearby fields as fertilizer, also contributes to the river’s algae issues.

Algae Shenandoah North Fork

Algae collects on the North Fork of the Shenandoah River near Bethel Road in Strasburg, VA, on July 22. (Courtesy of Friends of the North Fork)

A 2017 report from the Environmental Integrity Project found that fields in the counties around the Shenandoah River received at least one and a half times more phosphorous than the amount needed by the crops harvested in those counties, which allows excess nutrients to run off into local waters.

“We have huge inputs of nutrients into the river that fuel both types of algal blooms,” said Phillip Musegaas, vice president of programs and litigation for the Potomac Riverkeeper Network. Meanwhile, “climate change is changing the river. We will see more blooms because of hotter summers and longer periods of low water.”

Frondorf, the Shenandoah Riverkeeper, said progress has been made on many of the farms that abut the river. The number of cattle herds with direct access to the river has gone down from 75 to about 15 since 2015, he said.

In 2020, the Virginia general assembly passed a bill that will require cattle operations with 20 or more bovines in their pastures to exclude the animals from streams with fencing starting in 2026. But the measure has several caveats related to whether the state meets its Chesapeake Bay pollution reduction goals in 2025 and whether there is adequate funding provided to help farmers install the fences.

“Algal blooms are hard to predict, sort of like the weather, but we know that nutrients always exacerbate the issue,” said Joe Wood, Virginia senior scientist for the Chesapeake Bay Foundation. “If we invest more in cleaning up nutrients to the Shenandoah River, the river will be better and so will the Bay.”

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