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National Aquatic Resource Surveys

National Lakes Assessment 2012 Key Findings

Lakes and reservoirs provide many environmental, economic, and public health benefits. We use lakes for drinking water, energy production, food and recreation. Fish, birds and other wildlife rely on them for habitat and survival. In the National Lakes Assessment (NLA), the U.S. Environmental Protection Agency (EPA) and its partners surveyed a wide array of lakes representative of those found in the U.S., from small ponds and prairie potholes to large lakes and reservoirs. The NLA is part of the National Aquatic Resource Surveys, a series of statistically-based assessments designed to provide the public and decision-makers with nationally consistent and representative information on the condition of the nation’s waters.

What is the condition of lakes across the country?

  • >35% Nutrient pollution: Nutrient pollution is a widespread problem across the country. About 1 in 3 lakes (35%) have excess nitrogen and 2 out of 5 lakes (40%) have excess phosphorus. Too much of the nutrients nitrogen or phosphorus can contribute to algal blooms, low levels of oxygen, and harm to aquatic life.
  • <1% Microcystin: An algal toxin, microcystin, is detected in 39% of lakes, but concentrations rarely reach moderate or high levels of concern established by the World Health Organization (<1% of lakes).
  • <1% Atrazine: The herbicide atrazine is detected in 30% of lakes but concentrations rarely reach the EPA level of concern for plants in freshwaters (<1% of lakes).
  • 31% Biological condition:  We find that 31% of lakes have degraded benthic macroinvertebrate communities, which include small aquatic creatures like snails and mayflies. Analyses show an association between nutrients and biological condition. Lakes with high levels of phosphorus are 2.2 times as likely to have a degraded benthic macroinvertebrate community and lakes with high levels of nitrogen are 1.6 times as likely to have a degraded benthic macroinvertebrate community.

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Are conditions getting better or worse?

A comparison of the 2007 and 2012 National Lakes Assessments indicates little change between surveys. In most cases, the percentage of lakes in degraded biological, chemical and physical condition did not change over this five year period, with a few notable exceptions.

  • 13% (Better) Lake drawdown: Drawdown of lake water levels, whether by natural process or through direct manipulation, can adversely affect physical habitat conditions. Between 2007 and 2012, the NLA shows improving conditions with 13% fewer lakes in the most disturbed condition.
  • 8.3% (Worse) Cyanobacteria: The NLA measured the density of cyanobacteria cells, which can produce cyanotoxins, as an indicator of toxic exposure risk. The analysis reveals worsening conditions, with 8.3% more lakes in the most disturbed condition in 2012 than in 2007.
  • 9.5% (Worse) Microcystin: The NLA shows a 9.5% increase in the detection of an algal toxin, microcystin. However, concentrations of this algal toxin remains low and rarely exceeds WHO recreational levels of concern (<1% of the population) in both assessments.
  • 18.2% (Worse) Phosphorus: A supplementary analysis of the NLA data finds that phosphorus has increased in lakes that were previously low in phosphorus. In 2012, there were 18.2% fewer low-phosphorus lakes than in 2007.

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What are we doing to address problems?

The NLA indicates that our lakes are under stress. In particular, the NLA suggests a need to reduce nutrient pollution to improve lake conditions. EPA is working on many fronts to reduce the severity, extent, and impacts of nutrient pollution in our nation’s lakes and other waters. These efforts involve overseeing regulatory programs, conducting outreach and engaging partners, providing technical and programmatic support to states, financing nutrient reduction activities, and conducting research and development. For more information on what EPA is doing to reduce nutrient pollution, visit

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National Lakes Assessment 2012 Photo Story

  • Loon swimming across a lake Healthy lakes enhance our quality of life.  We use lakes for drinking water, energy production, food, and recreation. 
    Fish, birds, and other wildlife rely on them for habitat and survival. (Photo: Hilary Snook, EPA)
  • Members of NLA 2012 field crew preparing boats for sampling Conditions in our nation’s lakes, ponds and reservoirs are reported in the EPA’s National Lakes Assessment 2012 (NLA), one in a series of National Aquatic Resource Surveys designed to provide nationally-consistent and representative information on the condition of the nation’s waters.
  • NLA 2012 sampling site locations across the contiguous United States Background: In the summer of 2012, 89 National Lake Assessment field crews sampled 1,038 U.S. lakes using consistent methods and following standardized quality assurance protocols.  The surveyed lakes were identified using stratified random sampling and are representative of those found across the country, from small ponds and prairie potholes to large lakes and reservoirs.
  • Cows entering a lake located in EPA Region 8 Nutrient Pollution: The NLA finds that high levels of the nutrients phosphorus and nitrogen are widespread in lakes. Nutrient pollution can  contribute to unsightly algal blooms, too little oxygen, potential harm to aquatic life and human health, and impaired recreation. Human activities such as poorly managed agriculture or suburbanization of watersheds can result in nutrient pollution.
  • Findings for Nutrients: The NLA finds that 40% of lakes are in most disturbed condition for phosphorus and 35% are most disturbed for nitrogen. Excess levels of these nutrients in lakes are associated with increased risk of degraded biological communities. 
  • Photo of a lake in the Coastal Plains ecoregion that was sampled during the National Lakes Assessment 2012 Trophic Condition: Eutrophication – an increase in nutrients that also produces excessive plant growth -- is a slow and natural part of lake aging.  Human influences can accelerate eutrophication and its effects, such as nuisance algae, murky water, low levels of oxygen, odor, and fish kills.  
  • Findings for Trophic Condition: Based on measures of chlorophyll-a used to estimate trophic status in the NLA, more than half of lakes are eutrophic or hypereutrophic (most disturbed).
  • Crew performing zooplankton sampling on a Rhode Island pond Biological Condition: The NLA 2012 finds that 31% of lakes have degraded communities of bottom-dwelling insects and small aquatic animals like snails and crayfish.  In 21% of lakes, communities of zooplankton (tiny animals in the water column) are in degraded condition.
  • Crew members launching boats for NLA 2012 sampling Physical Habitat: The condition of lakeshore habitats provides important information on lake health.  Healthy lakeshore habitat slows pollution runoff and provides varied and complex ecological niches for aquatic life.  More than one quarter of U.S. lakes are in most disturbed condition for vegetation along the lakeshore and at the land-water interface. (Photo: Hilary Snook, EPA)
  • Algae growing in a pond in Delaware Recreational Condition – Algal Toxins: Algae and cyanobacteria are a natural part of freshwater ecosystems. However, some algae blooms, powered by high levels of nutrients and warm temperatures, can be harmful to people and animals.  An algal toxin, microcystin, is detected in 39% of lakes, but concentrations reach levels of concern in less than 1% of lakes. (Photo: Ellen Dickey, DNREC)
  • Crew members collecting a sediment core from a New England lake Recreational Condition – Atrazine and Mercury: The NLA looked at other indicators of recreational condition in lakes: atrazine, a widely used agricultural herbicide, and mercury in sediment.  Atrazine was detected in 30% of lakes although at levels of concern in less than 1% of lakes; 40% of lakes are in most disturbed condition for methylmercury in sediment. (Photo: Hilary Snook, EPA)
  • Field crew pouring a lake water sample into a collection bottle Change in Lake Condition: A comparison of the results of the NLA 2012 to those of an earlier study in 2007 show little change in lake condition between surveys.  However, one area of change is in the detection of microcystin, which increased by nearly 10%. Another difference emerged through additional  in-depth analyses of nutrient data.  While we did not observe changes in the nutrient condition categories, analysts found a dramatic 18.2% decline in the percentage of oligotrophic lakes (<10 µg/L of total phosphorus). (Photo: Hilary Snook, EPA)
  • Serene lake with crew preparing NLA field sampling equipment on dock Summary: The NLA 2012 was conducted by EPA in partnership with states and tribes.  It provides a number of findings that national, state, and local water resource managers can use to protect and restore lakes and reservoirs.  To read the NLA, visit the NLA 2012 national results and regional highlights page. To learn more about lake conditions in your region, visit the NLA interactive data dashboard