The occurrence of massive floating blue-green algae blooms in Liberty Lake beginning in the 1960s has prompted its citizens to seek advice on ways to improve water quality in the lake. This irreplaceable resource had once been a beautiful, clean, clear lake heavily used by area fisherman, boaters, swimmers, and picnickers. However the natural eutrophication process of the lake was being speeded up by human activities, and the water was starting to lose its clarity. If left alone, Liberty Lake would soon have become unfishable, unswimmable, and unusable. The surface was covered by slimy blue-green algae and decaying weeds for longer periods of time each year. Residents became concerned about the continued deterioration, and started asking questions about lakes, taking water samples for testing, becoming knowledgeable about the causes of lake problems and exploring possible solutions. At the same time residents became concerned about the continued deterioration and were beginning to realize the extent of the environmental problems facing them, people all across the nation were becoming aware of the limits of the environmental resources. Lakes and rivers throughout the country, to some degree, are showing the negative effects of human’s impact, and there are responses at the national, state, and local levels to this growing environmental awareness (Liberty Lake Sewer District, 1989).
Many Washington lakes and even some rivers have problems with excessive growth of algae. Algae can be smelly and unsightly as well as being toxic to humans, pets, and livestock. Algae grow rapidly when sunlight, temperature, and nutrients are adequate. Within only a few days, a clear lake can become cloudy with algae. When an algal species reproduces rapidly and reaches high concentrations, it is called an algae “bloom”.
There are many types of algae. Most are harmless, some are considered nuisances, and others are important to lake productivity. Blue-green algae are actually bacteria called cyanobacteria. They can create problems when they form blooms. The blooms happen mostly in the summer or fall, but can occur anytime. Blue-green blooms may float to the surface and can be several inches thick near the shoreline. A blue-green algae bloom often looks like green paint floating on the water and is hard to pick up or hold. Blooms of algae can give water an unpleasant taste or odor, reduce clarity, and color the lake a vivid green, brown, yellow, or even red, depending on the species. Filamentous and colonial algae are especially troublesome because they can mass together to form scums or mats on the lake surface. These mats can drift and clog water intakes, foul beaches, and ruin many recreational opportunities (Washington State Department of Ecology Freshwater Algae Website).
In general, there are a number of environmental factors that influence algal growth. The major factors include:
- the amount of light that penetrates the water (determined by the intensity of sunlight, amount of suspended material, and water color);
the availability of nutrients for algal uptake (determined by source and removal mechanisms);
- water temperature (regulated by climate, altitude, etc);
- the physical removal of algae by sinking or flushing through an outflow;
- grazing on the algal population by microscopic animals, fish and other organisms;
- parasitism by bacteria, fungi, and other microorganisms; and
- competition pressure from other aquatic plant for nutrients and sunlight
However, it is a combination of these and other environmental factors that determine the type and quantity of algae found in a lake. These factors are almost always in a state of flux, where change of seasons, development in the watershed, and rainstorms constantly create “new environments” in a lake.
Typical blue-green algae blooms observable in Liberty Lake primarily consist of Gloeotrichia, Anabaena, Microcystis and Aphanizomenon (EPA, 1982).
Examples of these blue-green algae colonies may be viewed at:
Of the nutrients necessary for algal growth, phosphorus is commonly the one that limits the amount of algae present. Phosphorus is taken up as Phosphate (PO4), which is the only inorganic form of phosphorus that organisms can use. If an overabundance of phosphorus comes into the lake faster than it can be assimilated, the result can be blue-green algae blooms.
Diverting the source of nutrients, both point and non-point sources, is certainly the best long-term solution to controlling the growth of algae in a lake. The results of this action, however, are not always immediate and supplemental methods may be required. One of these techniques is chemical inactivation and precipitation (Alum).
Alum (aluminum sulfate, Al2(SO4)3·18 H2O) has been used successfully to control internal phosphorus loading and improve water clarity in lakes. The alum can form an Al(OH)3 “blanket” over the sediments, reducing P release from the sediments to the water column. When aluminum sulfate [Al2(SO4)3·18 H2O)] is added to the water, a reaction occurs that produces aluminum hydroxide [Al(OH)3]. Through a series of subsequent reactions the phosphorus is either precipitated out of solution as aluminum phosphate (ALPO4) or by sorption onto the surfaces of the aluminum hydroxide polymers. Internal loading supplies significant phosphorus to the water column, the alum treatment should reduce water column phosphorus and thus planktonic algae, resulting in increased water clarity (Informational Handout, author unknown).
Cyanobacteria Toxicity Information
Blue-green blooms can pose a human health concern. Although most blue-green blooms are not toxic, some blue-green algae produce nerve or liver toxins. Toxicity is hard to predict in part because a single species of algae can have toxic and non-toxic strains. Also a bloom that tests non-toxic one day can turn toxic the next day.
People may become ill after swimming or water skiing in lakes with toxic blue-green algae. Rarely, humans may experience stomach pains, vomiting, diarrhea, and skin rashes. Nerve and liver damage have been observed following long-term exposure such as drinking water with toxic blooms. Pets and wildlife have died after exposure to toxic blue-green algae in Washington lakes, but worldwide there are no confirmed deaths of humans from algal toxins.
Three genera of cyanobacteria account for the vast majority of blooms, including toxic blooms, world-wide: Anabaena, Aphanizomenon, and Microcystis – sometimes referred to as Annie, Fannie, and Mike. In Washington, Aphanizomenon does not seem to produce toxic blooms, although the other two genera have produced toxic blooms in Washington lakes. A bloom can consist of one or a mix of two or more genera of cyanobacteria.
Types of toxins
Cyanobacteria can produce several toxins, but two types of toxins are of particular concern and are tested for: Microcystins and Anatoxin-A. Microcystins are a group of hepatoxins (toxins that affect the liver). Microcystins are very stable and do not break down quickly in water. Microcystins are considered to be the most commonly-found cyanobacterial toxins in water and are the toxins most responsible for human and animal poisonings.
Anatoxin A is a potent neurotoxin (toxins that affect the nervous system) which can cause lethargy, muscle aches, confusion, memory impairment, and, at sufficiently high concentrations, death (Washington State Department of Ecology Freshwater Algae Website).
IS A PARTICULAR BLOOM TOXIC?
Not all cyanobacteria blooms are toxic. Even blooms caused by known toxin-producing species may not produce toxins or may produce toxins at undetectable levels. Scientists do not know what triggers toxin production by cyanobacteria. Just a few years ago, it was believed that only about 10 percent of all blooms produced toxins. Recent studies have shown that the probability that an individual bloom containing Anabaena, Microcystis, and/or Aphanizomenon will be toxic is greater than previously thought (45-75%). Since cyanobacteria toxins can be lethal to pets in relatively small amounts, caution should always be taken when a bloom occurs.
Signs that a cyanobacteria bloom is toxic may be large numbers of dead fish, waterfowl, or other animals within or around a body of water. Terrestrial animals found dead may have algae around the mouth area or on the feet and legs, indicating possible ingestion of and contact with a toxic bloom.
Symptoms from sub-lethal poisonings differ with the kind of animal, nature of toxin, and quantity of toxin consumed. Any sudden, unexplained animal illness or death occurring near a water body containing a bloom should be suspect. There have been no confirmed deaths in humans due to consumption of bloom toxins. However, some blooms have caused “outbreaks” of dermatitis (a form of “swimmers itch”) and attacks of gastroenteritis in groups of swimmers. These causative agents appear not to be the same toxins as the potentially lethal toxins.
Only laboratory tests can confirm whether a bloom is toxic or non-toxic. If you live in Washington state and you want to report a cyanobacteria bloom and have it tested, please visit https://ecology.wa.gov/Water-Shorelines/Water-quality/Freshwater/Freshwater-algae-control (Washington State Department of Ecology Freshwater Algae Website).
Alum treatments, conducted by Washington State University, occurred in Liberty Lake in 1980-1981. The treatments were successful as clarity increased from a few inches to meters. Intense algae blooms occured in the 1960s and 1970’s, where the algae blooms were so pervasive that the entire lake surface would be covered for weeks at a time. The blooms shaded the weeds from the sun, causing them to die and float to the surface in large dark mats.
Liberty Lake today is in an improved condition after an intensive restoration project in the late 70s and early 80s; including the building of a sewage treatment system, dredging a 50 acre parcel to remove a two foot layer of nutrient rich sediment, and an alum treatment. Ongoing lake protection activities, monitoring, and water quality studies are conducted by Washington State University and the Liberty Lake Sewer and Water District to protect the lake’s water quality and aesthetic beauty.
Although Liberty Lake may still display algae blooms from year to year, the overall intensity and duration of the blooms are not as pervasive as earlier pre-restoration blooms.