More than half of the country’s rivers and streams are unable to support healthy populations of aquatic insects and other creatures, a survey of nearly 2,000 locations by the Environmental Protection Agency reported Tuesday.

The study found more than 55 percent of the rivers and streams “in poor condition, 23 percent in fair shape, and 21 percent in good biological health,” The Associated Press noted. High levels of nutrient pollution—phosphorous and nitrogen from farms, cities and sewers—were found in the waterways. Phosphorous was found in 40 percent of rivers and streams.

Land development along waterways was found to have enabled erosion, flooding and the introduction of pollutants as well.

“This new science shows that America’s streams and rivers are under significant pressure,” said Nancy Stoner, acting assistant administrator of the EPA’s water office. “We must continue to invest in protecting and restoring our nation’s streams and rivers, as they are vital sources of our drinking water, provide many recreational opportunities and play a critical role in the economy.”