Algaecides are chemicals used to directly kill algae. The Latin root is simple – algae, or microscopic plants, and cide, a killing agent. By far the most common algaecide is copper, in use for over 100 years and very effective against a wide range of algae. There are many formulations, with differences mostly intended to improve effectiveness or duration of activity under various environmental conditions, but the key ingredient remains the copper ion itself. After reactions are complete, the copper remains, and is usually deposited in the sediment. This can’t be good for the lake, but there are few studies that have demonstrated any measurable negative impacts. With repeated treatment, the sediment may be considered hazardous waste if ever dredged, but for the most part the reacted copper appears to be inert. Doses of copper in New England waters rarely exceed 0.2 mg/L as copper, and are often <0.1 mg/L. Larger doses are used in some other parts of the USA, mainly to overcome interference by high suspended or dissolved solids, and these are poor examples to compare with New England applications. Some zooplankton and some trout species may be susceptible to toxic effects at applied doses, but the vast majority of non-target aquatic organisms are not threatened by copper doses used in New England.

A more recent algaecide is peroxide, formed from sodium carbonate peroxyhydrate when added to water. It is an oxidant that impacts cell walls of algae, with groups like cyanobacteria being generally more susceptible than stronger walled forms like some greens and diatoms. It leaves no potentially hazardous residues. The primary drawbacks are that sometimes we want to kill green algae, especially mats of filamentous forms, and peroxide-based algaecides are more expensive than copper alternatives. Still, the generally positive environmental profile of peroxide-based algaecides makes them attractive. Peroxides seem to be more effective than copper on cyanobacteria mats, which are often sources of taste and odor in reservoirs.

There are a few other manufactured algaecides that have specialized applications, but copper and peroxide represent nearly all the market for this type of treatment. It is preferable to limit nutrients to control algae, but this is much easier said than done, and having algaecides as a management option helps make our drinking water safe and our recreational lakes swimmable. Excessive use of algaecides should be avoided, and control of nutrients should be pursued as a long term solution, but algaecide application is a valuable management tool that should not be rejected without careful consideration.

The biggest issue with treatment is the tendency to wait until there is a major accumulation of algae to treat. At that point treatment will lead to a lot of decaying organic matter, release of nutrients, and possibly release of toxins. This latter possibility has led many states to disallow treatment if potentially toxic algae are too abundant. The most effective way to use algaecides is to prevent a bloom, not get rid of one. This means tracking algae on a regular basis, typically weekly, and reacting when problem species start to increase, which is not an easy task.

One other important point about algaecides warrants attention. As noted at the start, these are compounds that directly kill algae. Some regulatory agencies, notably but not exclusively in New York, have defined algaecides as any additive that prevents algae from becoming abundant. Consequently, phosphorus inactivation with aluminum or lanthanum is considered to be algaecide application, and since these are not registered as algaecides with the federal government, treatments using them cannot be permitted. By this line of reasoning, addition of oxygen to the bottom of a lake to keep phosphorus sequestered is also an algaecide application, and addition of water to cause dilution or flushing in a lake would also represent application of an algaecide. This sort of regulatory foolishness hurts sound lake management and highlights why it is institutions that limit success far more than science or economics.

Monitoring Algae

How can one know what algae are in the water? Sometimes the growths are large enough that someone can see enough with the naked eye to make at least a preliminary identification, but for the most part algae identification requires the use of substantial magnification. For many years (literally over 200) we have used lens systems organized into what we call a microscope to magnify algae enough to tell what they are, and there are few substitutes for looking. Even then, considerable training is needed to know what is being observed, leading to bottlenecks in getting algae data to support lake management. Having a trained phycologist (one who studies algae) look at algae under a microscope remains the most preferred option, but some useful substitutes have arisen with digital technology. A digital microscope can magnify an image on a screen for under $1000. That image can be captured as a photo that can be compared with online sources or sent to an expert. The USEPA, Region I, has been pioneering an effort to get lake groups with an interest in harmful algae blooms to use such systems to report algae in their lakes. The accumulation of images can be turned into useful data that allow characterization of bloom frequency, common bloom species, and possibly trends within or among lakes.

The advent of automated systems for detecting and photographing particles makes it possible to process samples quickly, but we are just getting to the point where image libraries can be used by instruments to actually make identifications. The FlowCam, made by Fluid Dynamics in Maine, counts particles and photographs them, allowing the user to catalog and identify them with some expertise. At even a rudimentary level, such systems allow fast assessment of possible threats to lake uses. The Imaging FlowCytobot, developed by Woods Hole MA scientists, has been adapted by PhycoTech of Michigan to actually make identifications, and this technology could meet the need for rapid but taxonomically detailed and accurate data generation. These instruments are expensive, but contracting for identification can be affordable.

While lack of images (visual or digital) limits identification, use of fluorescence systems to determine the amount and types of pigments present can help discern algae blooms. Chlorophyll-a, a photosynthetic pigment common to all algae, can be assessed with fluorescence, which is basically the amount of light at a particular wavelength emitted from a water sample after excitation by light at another wavelength. The amount of chlorophyll-a in different types of algae varies, so this is not a direct measure of biomass, and the quality and amount of natural light and the concentration of non-photosynthetic organic matter in the water can cause variation not related to algal biomass. However, in a general sense, fluorescence can be used to get a rough appraisal of how much algae is in the water. Further, phycobilin sensors that detect pigments specific to cyanobacteria and provide an estimate of how much cyanobacteria are in the sample. There are even more sophisticated systems that excite samples with a range of wavelengths and record fluorescence in a way that allows a relative approximation of multiple algae types in the sample. Calibration and “training” of the instrument for specific waterbodies improves reliability.

Compared to identification and mapping of rooted aquatic plants, algae assessment is more challenging, but effort is needed if one wants to understand all important aspects of a lake.

NECNALMS 2017 Conference

Come join us this Friday and Saturday for our annual 2017 NEC NALMS Conference, New England Waters: Real World Watershed Monitoring and Management Options! This year, our conference will be hosted by URI Watershed Watch, the New England Chapter of North American Lake Management Society, and Save The Lakes, Rhode Island’s Association for Lakes. The conference will take place this Friday, June 9th, and Saturday, June 10th, in Kingston, Rhode Island at the University of Rhode Island’s Center for Biological and Life Sciences. Friday will consist of workshops and the NEC-NALMS meeting, while Saturday will have general sessions and a tour of the EPA Mobile Lab. Both days will have other optional events, such as dinner and a paint and sip! Please help us accomplish our goal of bringing together New England’s citizens, scientists, and professionals to share information and experiences in order to help restore and protect our lakes and watersheds! For more program and cost information, please visit our website or contact We look forward to seeing you there!