What's Going on with Clear Lake? Some questions and answers

For the first time in nearly twenty years, the summer of 2009 was marked by a population explosion of cyanobacteria (AKA "blue-green algae") in Clear Lake. These organisms multiply, rise to the surface, and die, then form thick mats of foul smelling decaying matter. To a much lesser extent, algal blooms recurred in 2010,with the worst infestations by far being in Clearlake and Clearlake Oaks.

2011 has been characterised by comparatively cool weather and high water levels, conditions which had been thought to be unpropitious for algal growth. The county also devoted substantial resources to palliative measures in the form of booms and aeration devices -- but nonetheless starting in mid July explosive growth of two different blue-green algae species occurred in many widely separated locations. In places where conditions are at their worst, virtually the entire water column has been occupied by algal growth. In other areas conditions may be much better than in previous years.

It is important to remember that both "true" algae and cyanobacteria are native to Clear Lake, and that their increased growth during warm weather is integral to the ecosystem of the lake. The problem is one of degree. Although the algae themselves are sometimes toxic, and people have been warned to avoid drinking untreated lake water or swimming in infested areas, the chief impact has been economic. Especially along the southern and eastern shores of the lake, algal mats have sometimes become so thick as to completely block shoreline access, and even where boating is possible the presence of this stinking nuisance has severely interfered with the normal recreational use of the lake by residents and visitors alike. Some resort owners effectively lost their entire summer season in 2009 and were also badly impacted in 2010 and 2011.

Everyone has questions. We hope to offer a few answers.

Why isn't the lake clear?
Clear Lake has never been clear, and never will be: the name is both a misnomer and a mystery. This shallow, warm body of water is naturally "eutrophic" (nutrient-rich) and thus supports a great deal of life -- which means lots of fish, lots of birds -- and lots of weeds and algae. In the words of Yuba College professor Dr. Harry Lyons, "Clear Lake is an emerald, not a sapphire."

Is sewage spilling into the lake?
No. Dead masses of cyanobacteria may look and smell like raw sewage, but they are something else altogether. Although overflows from sanitary waste pipes during heavy rains have been documented on a number of occasions these are winter occurrences, and regular testing reveals nothing that would indicate an ongoing sewage spill.

Is it safe to drink the water?
Not straight from the lake (as if anyone would think of doing that!) Tap water from public utilities has been treated and is perfectly safe to drink and use for cooking. Shallow wells near the lakeshore may be impacted and should be tested if there's any doubt about their safety.

Are there possible health effects from contact with cyanobacteria?
Yes. Close contact can result in a rash, irritated eyes, or respiratory symptoms; accidental ingestion could lead to nausea or other intestinal effects. For these reasons the Department of Environmental Health has issued a warning advising people to avoid swimming, wakeboarding, water-skiing, or jet-skiing in areas where algal mats or green scum are present. However, there have been no medically confirmed cases of illness associated with blue-green algae exposure in Lake County.

Will algae infested water harm my pet?
It could: pets should not be allowed to swim in areas where algae blooms are visible, or to drink the water in those areas.

What caused the algae bloom?
Many factors seem to have come together to create a perfect storm for cyanobacteria in 2009, starting with three years of drought. Low water levels, unusual springtime water clarity, climatic conditions that encouraged different levels of lake water to mix, exceptionally hot weather in July -- all played a causative role.

Why are there so many dead fish?
Low oxygen levels cause fish kills every summer, particularly on the South Shore. By further reducing normal late-summer low-oxygen levels, heavy algae growth can make the die-off particularly severe.

How can we get rid of the algal mats?
The best way for lakeshore residents and resort owners to disperse algal mats seems to be to spray them with strong jets of water, thus breaking them up and -- very important! -- adding extra oxygen. Several proposals have been put forward about ways to skim the algae off for removal, with the possibility of putting this unwelcome organic material to beneficial use as fertilizer or even as a source of biofuel, but so far none of these ideas have checked out in reality.

Isn't pollution really to blame?
Yes and no. Detrimental human activities have impaired Clear Lake water quality by increasing levels of both heavy metals (especially mercury) and nutrients, and the lake is listed by the state water control board as an impaired water body. There is no question that these forms of pollution are real, and that they have been linked to cyanobacteria population growth. A great deal of work needs to be done to return the lake to a healthy balance. But on the other hand chronic pollution that has existed for many years cannot explain the drastic algae bloom that occurred this summer, since the same stresses have been present in previous years when no significant algal growth was noted. Over the long run, the lake has been getting cleaner. It is certainly in far better condition than in the 1950s and 60s, when a combination of septic system seepage and applications of heavy pesticide sprays in an attempt to control gnats earned Clear Lake a mention -- as a horrible example! -- in Silent Spring. Banning DDT, construction of modern sewage treatment facilities, and implementation of a strong grading ordinance have done a lot to clean things up since then.

What can be done to improve the health of the lake in the future?
Many many things, big and small. To start with the big ones, the Middle Creek Project will restore 1200 acres of wetlands north of Rodman Slough, thus restoring natural filtering processes. Cleanup of the Sulphur Bank Mercury Mine Superfund site will remove (or at least drastically reduce) what is by far the most significant source of heavy metal pollution into the lake. Both of these projects need a great deal of money to become a reality. Increasing sewage system capacity and preventing future spills is also very important, so it's encouraging to learn that the county is in the process of constructing a new sewer line to service the section of the South Shore where so many spills have occurred in recent years. Continuing monitoring, erosion control, minimizing agricultural runoff, and streambed restoration are all important prescriptions for a healthy lake, as are efforts to increase areas of natural vegetation along the lakeshore. If you are a rimland property owner, plant tules!

How can I learn more?

  • Attend Clearlake TMDL ("Total Maximum Daily Load") stakeholder meetings: contact County Water Resources Engineer Tom Smythe for details.
  • Join a watershed group: more info from Watershed Coordinator Greg Dills.
  • Read the Clear Lake Nutrient TMDL, Monitoring and Implementation Plan, and other relevant information posted to the County website
  • Read Supervisor Denise Rushing's 2010 commentary, "What the lake is telling us."
  • Learn how tule revegetation can help the lake heal itself

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