To assess U.S. water resources, the U.S. Geological Survey (USGS) divides the nation into 22 hydrologic regions, or watersheds, based on the flow of water throughout the country. Each watershed represents a major river drainage area (e.g., the Missouri region) or combines rivers’ drainage areas (e.g., the Texas-Gulf region which includes several rivers draining into the Gulf of Mexico).
Even locations that are far from bodies of water are part of a hydrologic region because chemicals released to groundwater, land, or air can be washed or carried long distances to surface waters. These discharges can affect living resources within an aquatic ecosystem. For example, some chemicals can persist in the environment and accumulate in the tissues of fish and other wildlife. These chemicals can become more concentrated as predators farther up the food chain eat these organisms, which may ultimately cause health problems for wildlife and humans.
All 22 watersheds are displayed in the Where You Live map. The chart below shows the ten watersheds with the most TRI chemical releases for 2021. Releases were the greatest in the Alaskan and Great Basin regions. In these regions, most releases were from metal mines.
Note: Chart shows the ten watersheds with the most TRI chemical releases in pounds.
The chart below shows the ten watersheds with the most TRI chemical releases per square mile. Releases per square mile are greatest in the Great Basin region, which encompasses much of Nevada and Utah. Releases from metal mines make up 91% of the releases in this region.
Note: Chart shows the ten watersheds with the most TRI chemical releases in pounds per square mile.
This page was published in March 2023 and uses the 2021 TRI National Analysis dataset made public in TRI Explorer in October 2022.