Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Scytonema (blue green algae)
Why are some lakes full of algae and thick plants?
Plants naturally grow in and around lakes, but sometimes lakes and ponds can get an overgrowth of plants, algae, or bacteria. In many cases, humans are responsible. Chemicals that are used on lawns and in agriculture (like nitrogen and potassium) wash into our water systems. Once there, plants and algae have a feast on this “food.”
Sometimes overgrowths of cyanobacteria (called “blooms”) can make the water scummy and turn it a blue-green color (or other colors). Cyanobacteria produce compounds that impact the taste and odor of water, make fish unpalatable, and even produce toxins that affect human health. Scientists are still studying the causes of these blooms.
Learn more:
Related
Why does my drinking water look cloudy sometimes? Why does my drinking water look cloudy sometimes?
Once in a while you get a glass of water that looks cloudy; maybe milky is a better term. After a few seconds it miraculously clears up! The cloudiness is due to tiny air bubbles in the water. Like any bubbles, the air rises to the top of the water and goes into the air, clearing up the water. The water in the pipes coming into your house might be under a bit of pressure. This causes gases (air)...
Why does it take so long to rinse the soap off my hands? What are hard water and soft water? Why does it take so long to rinse the soap off my hands? What are hard water and soft water?
Water is said to be soft if it has a low concentration of calcium and magnesium ions in it, while hard water has a high concentration of calcium and magnesium. The minerals in hard water often react with most soaps to create a "soap scum," which is an insoluble substance that can temporarily adhere to your hands or the shower walls. When using hard water, you may have a harder time working your...
Where can I find information about my local drinking water supply? Where can I find information about my local drinking water supply?
The best way to learn about your local drinking water quality is to read the annual drinking water quality report/consumer confidence report that water suppliers now send out by July 1 of each year. The reports are often sent out with water bills, but they may be sent separately. The reports tell where drinking water comes from, what contaminants are in it, and at what levels. The U.S...
What can cause our water to have an earthy odor or to smell like rotten eggs? What can cause our water to have an earthy odor or to smell like rotten eggs?
Naturally-occurring organic compounds are created when plant material decays in lakes and reservoirs. Those organic compounds frequently cause musty, earthy odors, especially toward the end of summer. The odors can be objectionable, but generally are not harmful to health. However, odors can be caused by other constituents as well, so you might want to call your local Health Department and mention...
What can be causing our drinking water to have a reddish color? What can be causing our drinking water to have a reddish color?
Your water might be affected by iron, which is a commonly-occurring constituent of drinking water. Iron tends to add a rusty, reddish-brown (or sometimes yellow) color to water. If the color is more black than red, your water might contain a combination of iron and manganese. Both of these metals can cause staining of plumbing fixtures, porcelain sinks, or laundry, but they are not known to cause...
Does the use of pesticides affect our Nation's water quality? Does the use of pesticides affect our Nation's water quality?
Pesticide use in the United States has increased because not only must we supply our exploding population with food, but crops and food are also grown for export to other countries. The United States has become the largest producer of food products in the world, partly owing to our use of modern chemicals (pesticides) to control the insects, weeds, and other organisms that attack food crops. But...
Cyanobacteria - Scytonema (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Scytonema (blue green algae)
Cyanobacteria - Phormidium (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Phormidium (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Phormidium (blue green algae)
Algal Toxin Photo
Creek filled with Algal Toxins is surrounded by plant life on both banks. Trees line the background.
Creek filled with Algal Toxins is surrounded by plant life on both banks. Trees line the background.
Cyanobacteria - Nostoc (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Nostoc (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Nostoc (blue green algae)
Cyanobacteria - Dolichospermum (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Dolichospermum (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Dolichospermum (blue green algae)
Algae Sampling in Rapid Creek near Rapid City, SD
U.S. Geological Survey hydrologists preparing periphyton algae samples from rocks collected in Rapid Creek.
U.S. Geological Survey hydrologists preparing periphyton algae samples from rocks collected in Rapid Creek.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. If you see a bloom, avoid the area.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. If you see a bloom, avoid the area.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is a bloom on the shore of Lake Dora, FL.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is a bloom on the shore of Lake Dora, FL.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
Related
Why does my drinking water look cloudy sometimes? Why does my drinking water look cloudy sometimes?
Once in a while you get a glass of water that looks cloudy; maybe milky is a better term. After a few seconds it miraculously clears up! The cloudiness is due to tiny air bubbles in the water. Like any bubbles, the air rises to the top of the water and goes into the air, clearing up the water. The water in the pipes coming into your house might be under a bit of pressure. This causes gases (air)...
Why does it take so long to rinse the soap off my hands? What are hard water and soft water? Why does it take so long to rinse the soap off my hands? What are hard water and soft water?
Water is said to be soft if it has a low concentration of calcium and magnesium ions in it, while hard water has a high concentration of calcium and magnesium. The minerals in hard water often react with most soaps to create a "soap scum," which is an insoluble substance that can temporarily adhere to your hands or the shower walls. When using hard water, you may have a harder time working your...
Where can I find information about my local drinking water supply? Where can I find information about my local drinking water supply?
The best way to learn about your local drinking water quality is to read the annual drinking water quality report/consumer confidence report that water suppliers now send out by July 1 of each year. The reports are often sent out with water bills, but they may be sent separately. The reports tell where drinking water comes from, what contaminants are in it, and at what levels. The U.S...
What can cause our water to have an earthy odor or to smell like rotten eggs? What can cause our water to have an earthy odor or to smell like rotten eggs?
Naturally-occurring organic compounds are created when plant material decays in lakes and reservoirs. Those organic compounds frequently cause musty, earthy odors, especially toward the end of summer. The odors can be objectionable, but generally are not harmful to health. However, odors can be caused by other constituents as well, so you might want to call your local Health Department and mention...
What can be causing our drinking water to have a reddish color? What can be causing our drinking water to have a reddish color?
Your water might be affected by iron, which is a commonly-occurring constituent of drinking water. Iron tends to add a rusty, reddish-brown (or sometimes yellow) color to water. If the color is more black than red, your water might contain a combination of iron and manganese. Both of these metals can cause staining of plumbing fixtures, porcelain sinks, or laundry, but they are not known to cause...
Does the use of pesticides affect our Nation's water quality? Does the use of pesticides affect our Nation's water quality?
Pesticide use in the United States has increased because not only must we supply our exploding population with food, but crops and food are also grown for export to other countries. The United States has become the largest producer of food products in the world, partly owing to our use of modern chemicals (pesticides) to control the insects, weeds, and other organisms that attack food crops. But...
Cyanobacteria - Scytonema (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Scytonema (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Scytonema (blue green algae)
Cyanobacteria - Phormidium (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Phormidium (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Phormidium (blue green algae)
Algal Toxin Photo
Creek filled with Algal Toxins is surrounded by plant life on both banks. Trees line the background.
Creek filled with Algal Toxins is surrounded by plant life on both banks. Trees line the background.
Cyanobacteria - Nostoc (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Nostoc (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Nostoc (blue green algae)
Cyanobacteria - Dolichospermum (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Dolichospermum (blue green algae)
Microscopic view of blue green algae sample. Some algae produce toxins that threaten the health and safety of living things that come in direct contact. Cyanobacteria - Dolichospermum (blue green algae)
Algae Sampling in Rapid Creek near Rapid City, SD
U.S. Geological Survey hydrologists preparing periphyton algae samples from rocks collected in Rapid Creek.
U.S. Geological Survey hydrologists preparing periphyton algae samples from rocks collected in Rapid Creek.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. If you see a bloom, avoid the area.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. If you see a bloom, avoid the area.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is a bloom on the shore of Lake Dora, FL.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is a bloom on the shore of Lake Dora, FL.
Harmful Algal Blooms
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. Pictured here is Binder Lake in Iowa covered in algal blooms.
Updated Date: April 14, 2026