On Aug. 5, 2015, the color of the Animas River in Colorado turned a rusty orange as millions of gallons of contaminated water flowed downstream.
The source of the contaminated water was the Gold King Mine, an abandoned gold mine located along one of the tributaries of the Animas River.
The United States Environmental Protection Agency explained the cause of the spill, stating that, "while excavating above the old adit, pressurized water began leaking above the mine tunnel, spilling about three million gallons of water stored behind the collapsed material into Cement Creek, a tributary of the Animas River."
The plume of toxic water has since flowed down the Animas River, depositing dangerous metals, such as lead, arsenic, cadmium and mercury along hundreds of miles through three states.
Metals such as these are not only harmful to the people, but also animal and plant life. As a result, several communities near the river faced water restrictions following the spill.
Water from the Animas River eventually drains into the Colorado River and flows through the Grand Canyon.
The water quality in the Animas River from the Silverton, Colorado, area to the Durango municipal water intake has returned to pre-event quality levels, the EPA has said. However, the contaminants that were released during the spill still pose a threat.
Heavy rain and thunderstorms that move over the region could stir up the dangerous metals that have settled on the riverbed since the spill occurred.
According to AccuWeather Senior Meteorologist Ken Clark, it can take just one heavy thunderstorm to increase the flow of a section of the Animas River.
An increase in water flow would kick up the contaminants resting on the bottom of the river and mix them in with the river water before they settle on the riverbed again.
As a result, levels of lead, mercury and arsenic could spike in the Animas River following heavy rains, bringing a renewed danger to people and wildlife near the river.
A thunderstorm does not have to track directly over the Animas River to increase the flow of the river and stir up the dangerous metals. Rainwater and runoff can enter the Animas through one of its tributaries, lowering the quality of the water over a section of the river.
"Odds are that somewhere along that river there will be episodes of good runoff," continued Clark.
Whenever this process happens, the contaminants from the Gold King Mine spill can advance farther downstream before settling back on the riverbed.
As a result, the contaminants from the toxic spill could impact areas that were not initially affected.
Additionally, some areas might experience another wave of poor water quality water, forcing more water restrictions until the water is suitable for use and consumption again.
The Gold King Mine is just one of many abandoned mines across the western United States.
"Experts estimate there are 55,000 such abandoned mines from Colorado to Idaho to California, and federal and state authorities have struggled to clean them for decades," according to The Associated Press.
Cost and legal liability complicate the cleanup process of abandoned mines, such as the Gold King Mine, they said.
In a press briefing held on Aug. 13, 2015, the EPA Administrator Gina McCarthy said, "EPA is here to take responsibility, we are seeing the river restoring itself and we are working through issues to ensure that it is cleaned up. We are in this for the long haul."