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: USGS Water Science School - Why are some lakes full of algae?

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Why is our porcelain sink stained brown?

The brown stain is from a large amount of iron in your water. It is closely related to simple rust that you see on metal, which is iron oxide. Your water probably comes from groundwater that filtered through rocks containing iron-rich minerals on its way to the well.

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...

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. If you use soft water, the ions react with your soap to produce a residue that feels like it is hard to wash off. If you use hard water, you will have a harder time working the soap up into...

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...

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...

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 or laundry...

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...

How does mine drainage occur?

Mine drainage is formed when pyrite (an iron sulfide) is exposed and reacts with air and water to form sulfuric acid and dissolved iron. Some or all of this iron can precipitate to form the red, orange, or yellow sediments in the bottom of streams containing mine drainage. The acid runoff further dissolves heavy metals such as copper, lead, and...
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Date published: December 16, 2019

Phosphorus and River Water Quality

Investigating the effects of historical phosphorus on current river water quality. 

Attribution: Water Resources
Date published: November 22, 2019

Global Study Finds Algal Blooms Intensifying in Freshwater Lakes Worldwide

A study of global freshwater algal blooms funded in part by a U.S. Geological Survey (USGS) Landsat Science Team (LST) Award has found that harmful blooms showing up more and more in various U.S. cities are intensifying in lakes worldwide as well.

Date published: May 15, 2019

USGS Kicks Off Innovative Project to Study Harmful Algal Blooms in New York

Monitoring Effort Supports State’s Initiative to Combat Potentially Toxic Blooms

Date published: October 18, 2018

Salty water causes some freshwater harmful algae to release toxins

USGS study of Lake Okeechobee algae gives new insight on South Florida coastal blooms

Date published: March 31, 2017

20 Years Researching Harmful Algal Blooms Supports Sustainable Water Supply in Wichita

Two decades of harmful algal bloom, nutrient and sediment research by the U.S. Geological Survey is helping to support Wichita’s long-term vision of a sustainable water supply into the future. Early warning indicators of harmful algal blooms have been developed for Cheney Reservoir, Kansas, according to a new USGS publication done in cooperation with the City of Wichita, Kansas.

Date published: January 31, 2017

Tracking the Bad Guys: Toxic Algal Blooms

Every few days, a fleet of satellites orbiting 700 kilometers above the Earth scans the continental United States to help keep Americans safe. But these eyes in the sky aren’t seeking terrorists or enemy combatants: they scrutinize lakes to locate problems of the microbial variety, namely cyanobacteria.

Date published: October 24, 2016

The Science of Harmful Algal Blooms

Building knowledge to protect ecological and human health

Date published: June 16, 2016

New Science Challenges Old Assumptions about Harmful Algal Blooms

First-of-its-kind survey shows that algal toxins are found nationwide.

Date published: February 17, 2016

Algal Toxins Detected in One-Third of Streams Assessed in Southeastern United States

USGS scientists have detected toxins known as microcystins produced by various forms of algae in 39 percent of the small streams assessed throughout the southeastern United States. Their recent study looked at 75 streams in portions of Alabama, Georgia, North Carolina, South Carolina and Virginia.

Date published: August 12, 2015

Key Study Launched to Understand Increased Algae Growth in Lake Tahoe

The U.S. Geological Survey and the University of Nevada, Reno, will study the cause of eutrophication, or increased algae growth, along the nearshore of Lake Tahoe. Supported by California’s Lahontan Water Quality Control Board, the investigation is in response to widespread concerns with water quality and ecological degradation of the lake’s nearshore environment.

Date published: April 7, 2015

Multiple Satellite Eyes to Track Algal Threat to U.S. Freshwater

Four federal agencies including the U.S. Geological Survey have joined forces in an effort to transform satellite data into vital information to protect the American public from freshwater contaminated by harmful algal blooms.

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August 2, 2017

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)

July 26, 2017

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)

Landsat Image of Cyanobacteria
November 2, 2016

Landsat Image of Cyanobacteria

Images from Landsat, and other satellites, help locate the blue-green swirls associated with cyanobacteria. Photograph credit: NASA.

Aerial View of Lake Okeechobee
November 2, 2016

Aerial View of Lake Okeechobee

An aerial view of Lake Okeechobee in Florida shows an algal bloom. A third of all lakes studied by the USGS contained toxins produced by similar blooms. Photograph credit: Nicholas Aumen, USGS.

USGS scientist collecting a sample from a cyanobacterial bloom.
October 24, 2016

Collecting a sample from a cyanobacterial bloom

USGS scientist collecting a sample from a cyanobacterial bloom from Milford Lake, KS; Sept. 2, 2011.

Photo of algal toxins in a creek
August 28, 2016

Algal Toxin Photo

Creek filled with Algal Toxins is surrounded by plant life on both banks. Trees line the background.

August 11, 2016

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)

August 3, 2016

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)

Algal Bloom on Upper Klamath Lake
July 24, 2011

Algal Bloom on Upper Klamath Lake

A view of an algal bloom in Upper Klamath Lake from field sampling boat.