What Causes Algae in Lakes?

It’s that nasty-looking gunk that skims the surface of your nearest lake or pond. And it’s not only gross-looking, but it can also be very toxic and harmful. So, what causes algae in lakes? Well, let’s dive deeper (pun intended).

What are Algae in Lakes?

Also known collectively as lake weeds, algae are aquatic plants. 

They are termed “weeds” because they are unwanted. They often pose aesthetic and environmental problems for creatures that live in and around lakes.

How Does Algae Get in the Lake?

Aquatic weeds often end up in the lake when pet owners dump their aquariums into a storm drain or into the lake.

Those who live around lakes sometimes plant lake weeds. They are attempting a beautification project. Unfortunately, plants like purple loosestrife, bulrushes, and cattails take over and choke the lake.

Waterfowl and storm-water runoff may bring in lake weeds. Boaters have also redistributed aquatic weeds.

Plants that naturally grow in and around lakes get overgrown. This includes algae and bacteria. Chemicals containing nitrogen and potassium are used on crops and lawns. These wash into lakes and rivers. They are food sources for algae.

Cyanobacteria produce toxins that affect human health. These blooms are under scientific study which is exploring their causes.

What Causes Algae in Lakes?

Lakefront property is typically overdeveloped. This encourages lake algae growth

Landscaping has removed trees and shrubs to give lakeside owners a clear lake view.

Lax water management has resulted in the proliferation of lake algae. Runoff from homes and cottages has often been adequately processed.

Over-fertilized lawns caused runoff of chemically-infused water.

This overloading of nutrients has increased aquatic weeds. Phosphorus from fertilizers stimulates algae growth.

Types of Freshwater Lake Algae

There are several types of algae. 

These include:

Algae are simple photosynthetic organisms. They have some plant characteristics. 

Algae are aquatic plants.  

Part of the Protista kingdom, their chloroplasts allow them to synthesize food by means of the plant process of photosynthesis.

Algae have a wide environment. While they are water organisms they can live in wet soil, seawater, water-laden rock, and freshwater.

Algae include seaweed, giant kelp, and pond scum. 

Algae can be single or multicellular organisms. They vary in size and color.

Green Algae (Chlorophyta)

These are mainly found in water--especially freshwater. They can also be found in oceans. Green algae have flagella. This allows them to eat organic matter. With their plant-like chloroplasts, they are self-sustaining, processing their food. Some green algae contain thousands of cells. These include the horsehair algae and sea lettuce.

Blue-Green Algae

Blue-green algae produce dangerous cytotoxins, neurotoxins, endotoxina, and hepatotoxins. These are dangerous to the human respiratory system, kidneys, and liver. They also attack the nervous system in humans and other animals.

Euglenophyta (Euglenoids)

Like green algae euglenophyta contain chloroplasts. Euglena lives in fresh and saltwater. They are unique as they do not have a cell wall. Instead, they have a protein-rich layer called a pellicle. Euglena eats unicellular organisms and carbon-rich foods.

Golden-Brown Algae and Diatoms (Chrysophyta)

There are 100,000 species of golden-brown algae and diatoms. These unicellular algae live in both fresh and saltwater. Diatoms are abundant, found in oceans as plankton. Golden-brown algae are very small. In the ocean, they are nanoplanktons. Golden-brown algae reproduce more rapidly than diatoms.

Fire Algae (Pyrrophyta)

Unicellular fire algae are found mostly in saltwater.  A few species live in freshwater. Fire algae use flagella to move in the water. There are two types: cryptomonads and dinoflagellates. Some fire algae are bioluminescent. They can be seen lighting up the ocean at night. Fire algae produce neurotoxins. These are harmful to humans and other organisms.

Red Algae (Rhodophyta)

Red algae are eukaryotic cells. They have neither flagella nor centrioles. Most red algae and found in oceans and tropical regions. Red algae do well on solid surfaces like reefs where you will see them attached to reef and other algae. Rhodophyta have a cell wall composed of cellulose and other carbohydrates. Some seaweed is actually red algae.

Yellow-Green Algae (Xanthophyta)

Unicellular yellow-green algae are rare. They do not reproduce quickly. There are only 450 to 650 species of yellow-green algae. Their cell walls are composed of silica and cellulose. They have only two flagella. Xanthophyta appears light green because their chloroplasts lack green pigmentation. Yellow-green algae live mostly in freshwater. A few species live in saltwater.

Brown Algae (Phaeophyta)

Brown algae are comparatively large and complex species of algae. They live in marine areas. They have both photosynthesis organs and differentiated tissues. Brown algae examples include giant kelp, sargassum, and rockweed. Some brown algae may be over 300 feet long.

Besides being classified by color, algae may be differentiated by where they are found.

Some species of algae are often called "pond scum" or "pond moss". They form unsightly greenish clumps on the surface of the lake.

Dangers of Lake Algae

Lake algae can harm the aquatic environment. They also affect the health of the ecosystem. When plants feed on the material in lakes they upset the balance of plant life and available nutrients. This negatively affects the health of the lake. Oxygen depletion causes fish to die.

Toxic algae blooms may kill wildlife and humans. 

Algae also restrict water flow leaving the lake stagnant. Stillwater looks and smells bad. Worse, it is a breeding ground for mosquitoes.

Preventing Algae in Lakes

If the lake shows signs of algae-like stagnant water or surface discoloration, it is a sign of algal bloom

The water should be tested for the presence of cyanobacteria. This monitoring can stop a bloom before it forms. Effective ways to stop algae bloom include installing fountains or aerators to keep the water moving.

Another method is to dispose of sewage, pet waste, and other nutrients algae will feed on.

Installing rain barrels reduces area runoff.

Xeriscaping increases groundwater filtering before it reaches the lake.

Planting native vegetation, as opposed to cement embankments, allows nature to grow around the lake.

Removing leaves and grass clippings prevents them from entering the lake and decomposing there.

By using phosphorus-free fertilizers and detergents, nutrient-rich runoff is eliminated.

Phosphorus-binding materials prevent nutrients from stimulating algae growth.

A water management specialist can monitor water quality and treat the lake if necessary.

Removing Lake Algae

Lake algae are soft. It can be skimmed, raked, or pulled. Algae can be removed mechanically but this can be very expensive.

Herbicides will affect the health of the lake, its plants, and animals.

Indicators Algae Should be Removed

Too Many Weeds

The profusion of algae is turning the water a bad color. There is an unpleasant odor and the water isn’t moving.

Too Much Muck

The buildup of silt, mud, or muck is a sign of a lack of aerobic bacteria on the lake bottom. There is a lack of oxygen.

 Clouded, Muddy Water

Excessive mud disrupts the photosynthesis cycle. This means an imbalance in the ecosystem of the lake. Muddy water is an eyesore.

Watershed erosion may result in runoff of dirt and wastes.

Zebra Mussels

Zebra mussels infest lakes. They reduce biodiversity and kill lakes.

Dying Fish

Dying fish often are a sign of depleted oxygen. Excessive algae buildup may be the cause. Dead fish may also be caused by blue-green algae, parasites, sewage runoff, acid rain, or bacteria.


The freshness of lake water quality is measured by e-coli levels caused by human and animal waste. Over 235 units per 100 milliliters of water is dangerous.

What Can GoodbyetoMuck do to Help?

Goodbye to Muck has products aimed at preventing unwanted lake algae. 

These LakeMats and MuckMats are eco-friendly. They can be placed on the lake bottom wherever algae exist. The mats block the light from the lake weeds preventing photosynthesis and causing the plants on the lake bottom to die.




Large MuckMat

12' x 24'

$569.00 / unit

Medium MuckMat

12' x 19'

$509.00 / unit

Small MuckMat

12' x 14'

$449.00 / unit

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