Overall, blue-green algae are true survivors in the environment. They have been around for roughly 3.5 billion years and have adapted themselves to almost every habitat on the planet in that time. Given that many lakes, reservoirs, and ponds in the world are nutrient enriched, often due to pollution, it is no wonder blue-green algae related problems are becoming more frequent.
Why should I be aware of blue-green algae?
Many of the common blue-green algae have the ability to produce toxins. These biochemical poisons come in two main forms, hepatotoxins (that primarily target the liver) and neurotoxins (that target the nervous system). Well over 100 different algal toxins have been identified to date, but the group referred to as microcystins are the most frequently observed as well as some of the more toxic metabolic compounds known. A large percentage of the public will report “allergic” type reactions after exposure to blue-green algae, such as intestinal problems, respiratory problems, or skin irritations. A number of the microcystins have also been implicated as tumor promoting compounds, which makes chronic exposures (low exposure over time) a growing concern.
Toxic blue-green algae have been documented from countries throughout the world. Published reports date back to the 1870s, although there are suggestive references back to antiquity. Livestock deaths are commonly reported in the literature, as well as cases of pets or wildlife dying after contact with lakes and ponds suffering a blue-green algae bloom. While no human deaths have been linked to blue-green algae blooms in the United States to date, many countries have reported outbreaks of gastroenteritis, liver problems, and some deaths as a result of contact with blue-green algae infested water.
The exact “triggers” in the environment that cause these algae to produce toxins have not been identified, although toxin production does seem to be correlated with increasing amounts of phosphorus in the water column (i.e., the overall level of nutrient enrichment). Another confounding factor is that some species, or strains within species, seem to adjust their toxin production to unknown environmental cues. Until the ability to test for the common algal toxins becomes widely available, it is best to assume a large blue-green algae bloom is toxic (especially when composed of species with a known history of toxin production) and take reasonable precautions.
What precautions and actions should I take?
If your water supply lake has an overtly visible blue-green algae bloom in progress, you will almost certainly have started getting taste and odor complaints from customers. The best course requires prior planning in the form of 1) having an alternate raw water source you can switch to, or 2) having an activated carbon filtration system in place for such occasions. Granulated activated carbon (GAC), when used after the standard sequence of water treatment steps, but pre-final chlorination, can provide almost 100% removal of taste and odor compounds including, presumably, any algal toxins. Particulate activated carbon (PAC) can be almost as effective if used later in the process stream, but before the final chlorination step.
Adding chemicals to the raw water, to kill the algae, is almost certain to release more of the undesirable compounds into the water and is,therefore, not recommended. Neither is treating the lake and bloom with herbicides, such as copper sulphate. When applied to a bloom in progress, herbicides release a great deal of the offending chemical substances into the water and make treatment even more difficult. Additionally, treatment could cause rapid oxygen depletion in the lake due to the sudden die off and decomposition of the algae. Lake aeration is often touted as a “cure” for algae blooms, but works best in small lakes and needs to be tailored to a lake’s specific ecology.