The Impacts of Harmful Algae in a Lake

Algal blooms are a result of an overgrowth of microscopic algae in water bodies, as Karina Lakefront Maintenance explains. They normally produce foul-smelling, foam, froth and are sometimes toxic, depending on the type of algae. These blooms derive energy from the sun for them to grow rapidly and are slowly appearing in most reports on freshwater harmful algal blooms. This is due to them becoming an environmental problem in freshwater ecosystems like ponds, rivers, lakes, and reservoirs.

Algal blooms, which come in various colors like brown, blue-green, yellow, pink, and red, are not all toxic, but the majority are. Harmful algal bloom, commonly referred to as HAB, is an algal bloom that produces toxins that can harm water bodies and both humans as well as other organisms.

They can form in ponds, freshwater bodies, lakes, and even swimming pools making the water smelly and slimy. Wide stretches of coastlines and closing beaches have been vastly affected resulting in the formation of a foamy brownish-red coloration known as a red tide in the sea.

Let’s take a look at the impacts of harmful algae in a lake especially on the environment and human health.

The Impacts of Harmful Algae in a Lake

HABs which occur both in saltwater and freshwater environments have various harmful effects both on the environment as well as organisms. One of the top impacts is as a result of the toxins HABs produce. These toxins can kill aquatic animals like fish or shellfish directly or may sicken wildlife or humans after the ingestion of contaminated seafood or water.

The second impact is environmental degradation due to the accumulation of high biomass during algal blooms.

High Health Risk

Depending on the toxins ingested or involved, HAB toxins can cause harm to humans through human food poisoning syndromes. Due to excess nutrients in lakes, the bacteria cyanobacteria also known as blue-green algae gets the nutrients it needs to grow thus leading to an overgrowth.

The high density of cyanobacteria and other harmful organisms leads to the accumulation of scum on the lake surface and sometimes even discoloration of the water and therefore, giving it the name harmful algal blooms (HABs).

According to research, the increased nutrient levels in a lake are a result of human activities and cyanobacteria thrive in such. HABs formation has been used as an indicator of excess nutrient concentrations.

Cyanobacteria produce toxins cyanotoxins, hepatotoxins, derma toxins and neurotoxins that are harmful both to aquatic animals like fish, humans, mammals and birds. Neurotoxins mostly affect the nervous system, hepatotoxins the liver and dermatoxins the skin.

Effects include depletion of dissolved oxygen in the water body once the algal cells decay, light attenuation and clogging of fish gills which kills fish. Once fish die, this alters the food web dynamics since fish are a source of food thus altering the energy flow within an ecosystem.

In turn, there is a decrease in biodiversity and temporary or permanent damage to important habitats.

The skin can also be affected due to skin contact with some toxins during swimming or exposure to those present in the air. This is dangerous especially when algal blooms occur in drinking water supplies. Cyanotoxins can pose a danger to livestock, pets, and people that come in contact with the affected water.

Increased Turbidity

Since algal blooms create a turbid (cloudy) underwater environment on water bodies. This prevents light penetration into the water and bottom-dwelling organisms, including plants. This affects organisms that depend directly or indirectly upon the underwater plants for their food supply and shelter.

Sick Animals

HABs release toxins that can not only make fish sick but disrupt the production of large-scale fish due to sickness and even death of the fish. Algal blooms mostly golden algal blooms have over the years been on the rise after they worked their way up the food chain.

Mammals, birds, and other wildlife that rely on grasses, shellfish, or fish as a food source have been affected especially when these sources are tainted with toxins.

Unsafe Drinking Water

Recently, HABs’ impacts were noticed on drinking water supplies around the world. In some states, algal toxins (microcystin) were found to have grown beyond the safety threshold for drinking water. As a result, many people were sickened with others left without drinking water for days.

Also, some facilities have been threatened by toxic and non-toxic HABs, due to the presence of neurotoxins and skin-irritating compounds in the treated water supplied to households. Some of the toxins even caused damage to plant operations after the toxic compounds clogged intake filters and foul membrane surfaces.

Statistics show that there is a high likelihood that people drinking water from lakes and reservoirs might be exposed to contamination by algal toxins. While some resort to boiling HAB-contaminated water this doesn’t destroy toxins and can instead increase their concentration.

It’s therefore recommended that drinking water should undergo drinking-water treatment processes to remove algal toxins. The processing facilities should also be well maintained to remove any bacteria that may remain in the water.

Hypoxic/Dead Zones

Toxic HABs are not the only ones with harmful impacts. Nontoxic HABs also have harmful impacts called dead zones which affect aquatic ecosystems. These are areas in a water body with little to no oxygen that cause the death of aquatic life. Hypoxic zones are a result of eutrophication. Bacteria and algae can die and decompose using up most of the surrounding oxygen leading to the death of other organisms due to suffocation.


The HAB crisis is something that should be looked into and solutions found to combat the problem. This will help to protect their people from exposure to toxic blooms and reduce the growing prevalence of HABs which are harmful to human health, wildlife health, ecosystems and the economy.

Mashhap Team


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