From the U.S. EPA:

The U.S. Environmental Protection Agency today released its most comprehensive study of the nation’s lakes to date. The draft study, which rated the condition of 56 percent of the lakes in the United States as good and the remainder as fair or poor, marked the first time EPA and its partners used a nationally consistent approach to survey the ecological and water quality of lakes. A total of 1,028 lakes were randomly sampled during 2007 by states, tribes and EPA.

“This survey serves as a first step in evaluating the success of efforts to protect, preserve, and restore the quality of our nation’s lakes,” said Peter Silva, assistant administrator for EPA’s Office of Water. “Future surveys will be able to track changes in lake water quality over time and advance our understanding of important regional and national patterns in lake water quality.”

The National Lakes Assessment reveals that the remaining lakes are in fair or poor condition. Degraded lakeshore habitat, rated “poor” in 36 percent of lakes, was the most significant of the problems assessed. Removal of trees and shrubs and construction of docks, marinas, homes and other structures along shorelines all contribute to degraded lakeshore habitat.

Nitrogen and phosphorous are found at high levels in 20 percent of lakes. Excess levels of these nutrients contribute to algae blooms, weed growth, reduced water clarity, and other lake problems. EPA is very concerned about the adverse impacts of nutrients on aquatic life, drinking water and recreation. The agency will continue to work with states to address water quality issues through effective nutrient management.

The survey included a comparison to a subset of lakes with wastewater impacts that were sampled in the 1970s. It finds that 75 percent show either improvements or no change in phosphorus levels. This suggests that the nation’s investments in wastewater treatment and other pollution control activities are working despite population increases across the country.

The results of this study describe the target population of the nation’s lakes as a whole and are not applicable to a particular lake. Sampling for the National Rivers and Streams Assessment is underway, and results from this two-year study are expected to be available in 2011.