America’s Rivers Have Become More Toxic in the Last 37 Years


A new study has shown that at least one-third of America’s rivers have changed color since 1984. Scientists believe the culprit is toxic algae blooms as a result of human activity.

According to a new study published in the journal Geographical Research Letters, satellite images since 1984 have consistently shown that at least one-third of tens of thousands of mile-long river segments have noticeably shifted color. The findings included 11,629 miles (18,715 kilometers) that became greener or went toward the violet end of the color spectrum. 

Dominantly Yellow to Distinctly Green

The study further showed that only about five percent of US river mileage is considered blue — a color often equated with pristine waters by the general public. In contrast, about two-thirds of American rivers are yellow, which signals they have lots of soil in them. Another 28 percent of the rivers are green, which often indicates they are choked with algae. The researchers also found that two percent of US rivers over the years shifted from dominantly yellow to distinctly green. The study lead author John Gardner, a University of Pittsburgh geology and environmental sciences professor, said”

“If things are becoming greener, that’s a problem.” 

The study looked at more than 230,000 NASA satellite images over 35 years, focusing on rivers and reservoirs. The research found much of the shift to greener rivers in the North and West, while the yellowing occurred more in the East and around the Mississippi River. It also found some rivers change colors naturally with the seasons. 

Produce Toxins |  In America’s Rivers

Gardener further said that while some green tint to rivers can be standard, it almost always means large algae blooms that cause oxygen loss and produce toxins. The leading cause of color changes includes farm fertilizer run-off, dams, efforts to fight soil erosion, and human-made climate change, which increases water temperature and rain-related run-off, the study authors said. 

For example, the green at times in the Ohio River indicates a harmful algae problem from farm runoff. At the same time, rivers that are getting less yellow demonstrate the success of regulations to prevent soil erosion. The study’s co-author Tamlin Pavelsky, a professor of global hydrology at the University of North Carolina, said: 

“We change our rivers a lot. A lot of that has to do with human activity.”

Outside experts praised the study, saying while hard-to-understand measurements have shown problems with American rivers, this illustrates the situation entirely. Martin Doyle, head of water programs at Duke University, said:


“The study is super cool and a bit mind-blowing (yet intuitive) […] it shows how almost every aspect of our planet is being affected by humans, now including the basic color of our water. That’s pretty profound if you think about it […]. It’s also important because it opens up the idea and potential of using river color as an early-stage indicator, or warning of environmental change.” 

Public Health and Aquatic Ecosystems

Harmful algal blooms don’t just affect our oceans. They also form in freshwater bodies, making lakes, ponds, or your favorite swimming hole smelly and slimy. Algal blooms are odious but more critical; they can also be dangerous, imperiling public health and aquatic ecosystems, and costly, affecting local economies. While they aren’t a new phenomenon, reports of freshwater harmful algal blooms have increased significantly over the past 40 years.

People can be exposed to toxins associated with algae blooms when they swim in or swallow affected waters, eat poisoned shellfish or fish, besides cooking with the water and inhaling droplets. Depending on the level of exposure and the type of algal toxin, health consequences may range from mild to severe to, in extreme cases, fatal. Pets and especially dogs are particularly vulnerable since they are likely to swim or drink that water. 

Threaten Public Health  ||  America’s Rivers

It is also estimated that between 30 million and 48 million Americans get their drinking water from lakes and reservoirs that could be periodically contaminated by algal toxins. And boiling HAB-contaminated water not only doesn’t destroy toxins but can, in fact, increase their concentration. 

Thankfully, drinking-water treatment processes can typically remove algal toxins, such as cyanobacteria. Still, if processing facilities aren’t well maintained and up to date, the bacteria may remain in the water. Inadequate treatment can compromise water quality, threaten public health, and disrupt or even shut down treatment plants. Knowing where Algae blooms are occurring—and whether the government is responding—is a critical first step to keeping our waterways, families, and ecosystems safe.



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