Lake Anne residents walking alongside the 30-acre lake in recent weeks might have noticed that the water has lately appeared unusually murky and is bright blue-green in color.
Other Lake Anne visitors might have caught a whiff of a foul, sewer-like odor emanating from the water near certain coves.
The greenish murkiness and stinky smell are believed to be the byproducts of an undesirably high volume of blue-green algae that have been flourishing in Lake Anne over the last few months.
While the increasing algae blooms do not pose a health hazard, they do create an environment that some may consider occasionally disgusting.
"I don't know what's going on with the water, but it appears to be a step backward," said Lake Anne resident Vicky Wingert, a member of Reston Association's Board of Directors, at a recent meeting.
Reston Association has received more than a few complaints and concerns about the lake's water quality, said Larry Butler, RA's director of parks and recreation.
"We're seeing a fairly long, sustained algae bloom," he said. "It can be gross, but it's not that big of a deal other than aesthetics."
RA HAS MONITORED the quality of all Reston's lakes for more than 20 years, but officials are paying particular attention to Lake Anne, which at 41 years is the oldest of its four local man-made lakes.
Six times each year, RA tests the lakes for temperature fluctuations, ion conductivity, water clarity, and measures the levels of dissolved oxygen and nutrients. RA officials regularly run the lakes through the tests to uncover long-term trends that point to the overall health of the water.
Though the most recent water quality report will not be completed until later this month or in January, Butler said it appears Lake Anne's bottom is packed with nutrient-rich sediment, contributing to the growth of the blue-green algae.
"Basically, the bottom of Lake Anne is a nutrient sink," he said.
The blue-green algae tend to congregate in areas of the lake where the water remains relatively calm, such as near the concrete steps at the plaza and along the canal under the Van Gogh Bridge.
When sunlight shines down on the algae biomass for a prolonged period of time, the algae essentially cooks and then rots. The rotting algae are believed to be the source of the foul smell.
"If you get enough algae backed-up into a cove, with the sun baking it, you're going to get that odor," Butler said.
SEVEN YEARS AGO, RA installed an aeration system to boost diminishing levels of oxygen, which are needed to sustain aquatic life. Initially, the lake's water appeared clearer and healthier, but now the system may be partly responsible for the increasing amounts of algae that started to appear over the last two years.
"I'm not a water quality expert, but it looks like things are getting worse," said Robin Smyers, the Lake Anne representative on RA's Board of Directors. "The canal in particular has gotten extraordinarily dirty."
Butler believes the sediment flow from nearby streams is compounding the problem, though RA is working to stymie the flow by restoring eroded stream banks.
In the summer of 2002, RA hired a contractor to dredge Lake Anne, but the $250,000 effort did not rectify the problem. Little can be done to reduce the nutrients already sitting at the bottom of Lake Anne, but the stream restoration efforts could prevent things from declining.
"We just want to keep things from getting any worse than it already is," Butler said.