Alpine glaciers, wild coastlines, temperate rainforests, and deep river valleys coexist on the Olympic Peninsula in the northwest corner of Washington state. Surrounded by blue waters, peaceful islands, and bustling population centers, its rugged interior remains a relatively remote bastion of wilderness.

The Olympic Mountains’ imposing terrain comes into focus in this oblique view of the region, captured by an astronaut aboard the International Space Station. The image is a composite, made of several sequential, overlapping photos fused together into a panorama. Olympic National Park encompasses the peninsula’s mountainous core, along with some stretches of the Pacific coastline. Much of the remaining area is either national forest, state-owned land, or tribal territory.

The rock making up the mountains mostly originated beneath the surface of the ocean. From about 55 to 15 million years ago, layers of basalt from undersea eruptions and sand and mud transported seaward by rivers accumulated on the ocean bottom. This material was scraped off the Juan de Fuca plate as it subducted beneath the North American plate, with rock layers crumpling and rising up to 8,000 feet (2,440 meters) above sea level.

Tectonic forces continue to push the mountains skyward, but the countervailing force of erosion in this rainy, snowy corner of the country effectively cancels out the uplift. Snow at higher elevations feeds glaciers that carve out underlying rock. Glaciers in the Olympics are retreating and thinning, however, and their numbers are declining. One study tallied 255 glaciers and perennial snowfields in the range in 2015 and found that 35 glaciers and 16 perennial snowfields had disappeared in the preceding 35 years.

Other erosion is evidenced by the deep valleys radiating out from the snowy peaks. The Hoh, Queets, and Quinault rivers, draining west into the Pacific Ocean (bottom of the frame), are prominent in this view. These verdant valleys are known for their temperate rainforests, and the ancient forest in the Hoh River valley was once considered among the most naturally quiet places in the U.S., uninterrupted by human-caused noise.

Flowing to the north, the Elwha River has a rich natural and human history, including some of the earliest Euro-American exploration of the Olympics. Sponsored by a Seattle newspaper, an expedition from December 1889 to May 1890 crossed the mountain range from north to south, traveling up the Elwha valley and down the Quinault. The party spent several months in the Elwha Valley, their progress hindered by an unusually harsh and snowy winter. 

In the early 1900s, entrepreneurs saw economic opportunity in the valley. Two dams constructed on the river produced power for local industry. But the structures came with costs, such as blocking the migration of once-abundant trout and salmon to their spawning grounds. In 2011 and 2014, the dams were removed in what was then the largest such project in the U.S., and the process of restoring fish populations, seeding native plant communities, and replenishing sediment along the riverbanks commenced.

The mouth of the Elwha forms a delta in the Strait of Juan de Fuca, the waterway bordering the peninsula to the north. The U.S.-Canada border runs through the middle of this 11- to 17-mile-wide (18- to 27-kilometer-wide) channel, with Vancouver Island in British Columbia lying to the north. The strait connects the Pacific Ocean with the Strait of Georgia and Puget Sound. Ship traffic uses the strait to access important West Coast ports, including Seattle and Tacoma, visible along the top-right edge of the image.

Astronaut photographs ISS047-E-104138 through ISS047-E-104144 were acquired on May 6, 2016, with a Nikon D4 digital camera using a focal length of 400 millimeters. They are provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit at NASA Johnson Space Center. The images were taken by a member of the Expedition 47 crew. The images have been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Story by Lindsey Doermann.

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References & Resources

• Fountain, A. G., et al. (2022) Glaciers of the Olympic Mountains, Washington—The past and future 100 years. Journal of Geophysical Research: Earth Surface, 127(4), e2022JF006670. 
• NASA Earth Observatory (2016, February 14) Olympic National Park. Accessed July 22, 2026.
• NASA Earth Observatory (2012, August 25) Restoration of the Elwha River. Accessed July 22, 2026.
• National Park Service (2026, July 7) Olympic National Park. Accessed July 22, 2026.
• Washington State Department of Natural Resources, Olympic Mountains. Accessed July 22, 2026.

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Editor’s Note: Today’s story is the answer to the July Puzzler.

Call it an alluvial face-off. On the southern end of Severny Island in the Russian Arctic, rivers rush down from rugged terrain flanking a broad valley. Upon reaching flatter ground, the waters slow and distribute sediment into cone-shaped features called alluvial fans. Several appear in opposing orientations alongside a braided river in this Landsat 9 image.

Severny Island (Ostrov Severnyy) is a mountainous, uninhabited landmass in the frigid high latitudes of the Northern Hemisphere. Part of the Novaya Zemlya archipelago, the island is largely covered in glacial ice. Some glaciers, especially in the north, terminate in the sea, while others end on land, feeding meltwater into glacial streams.

Sediment-laden streams, along with the island’s topography, create favorable conditions for the formation of alluvial fans. The features typically appear at the base of steep mountain ranges, where narrow river channels open onto flatter terrain. There, rivers can slow, divide into smaller channels, and deposit sediment. Over time, the channels migrate back and forth to build up fan-shaped deposits. Dueling fans line several northwest-southeast-trending valleys in the wider view below.

Seasonal snowmelt and glacial runoff likely keep Severny’s rivers supplied with ample fan-building material. Hydrologists note that higher river flows during the warmer months, driven by snowmelt, can carry more sediment out of the mountains. Glaciers also produce large volumes of eroded material as they grind downslope, some of which flushes out in meltwater.

Smaller, land-terminating mountain glaciers, like those on southern Severny Island, are particularly prone to melting as the atmosphere warms. Severny’s ice is relatively understudied due to its remoteness, but satellite observations give scientists an understanding of its health. Recent analyses incorporating digital elevation models found that land-terminating glaciers across the Novaya Zemlya archipelago thinned during the 2000s and 2010s, especially at lower elevations.

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.

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References & Resources

• Małecki, J. (2022) Recent contrasting behaviour of mountain glaciers across the European High Arctic revealed by ArcticDEM data. The Cryosphere, 16, 2067–2082.
• Melkonian, A.K., et al. (2016) Recent changes in glacier velocities and thinning at Novaya Zemlya. Remote Sensing of Environment, 174, 244-257.
• NASA Earth Observatory (2009, July 30) Novaya Zemlya. Accessed July 13, 2026.
• National Geographic Society (2023, October 19) Alluvial Fan. Accessed July 13, 2026.
• Science Education Resource Center, Carleton College (2026, June 9) Cold climate conditions as a driver of alluvial fan deposition in the Lost River Range, Idaho, USA. Accessed July 13, 2026.

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From declines in annual sea ice extent to the greening of the tundra, environmental change has been unfolding incrementally in the Arctic over decades. Some shifts, however, have come on more abruptly.

Satellite, aerial, and ground-based surveys spanning more than 600 miles (1,000 kilometers) across Alaska’s Brooks Range have observed stream water changing from clear to orange in more than 200 watersheds. What’s more, scientists are finding that the switch has largely taken place within the past 10 to 12 years, coinciding with a pronounced increase in air and ground temperatures.

Thawing permafrost soils, accelerated by warming air and ground temperatures, are the most likely cause of the “rusty” rivers, scientists say. They surmise that water is now encountering thawed ground and bedrock where it previously had not. Chemical weathering of minerals leaches iron, sulfuric acid, and trace metals into streams, akin to the process behind acid mine drainage, which similarly pollutes and discolors water near abandoned mines. Microbes may also contribute to the color change by producing a soluble form of iron as they digest plant and animal matter in thawing soils, which then becomes oxygenated, or “rusts,” in flowing streams.

Researchers have only recently begun to comprehend the prevalence of rusting rivers in Arctic regions. In 2024, a team of National Park Service, U.S. Geological Survey, and university scientists documented 75 northern Alaskan streams that recently changed from clear to orange. With subsequent exploration, mostly using high-resolution satellite imagery, they added 200 more observations. The locations of these discolored streams, published in NOAA’s 2025 Arctic Report Card, are shown in the map above.

“I’m still surprised by the broad spatial scope of our observations,” said Brett Poulin, environmental toxicologist at the University of California, Davis. He and his collaborators have been monitoring the region’s streams since 2013—when many were still clear. “Now we’re seeing hundreds of streams that have changed color seemingly overnight, including in designated National Wild & Scenic River corridors,” he said.

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The Agashashok River in Noatak National Preserve is one of many streams in Alaska whose water has turned from clear to rusty orange. The change appears in these images, acquired on July 12, 2017 (left), and July 20, 2020 (right), by the OLI (Operational Land Imager) on Landsat 8. NASA Earth Observatory images by Michala Garrison.

Observations from NASA/USGS Landsat satellites allowed the team to determine the timing of several of these changes. For the 2024 study led by ecologist Jon O’Donnell of the National Park Service, the team calculated a redness index based on red and blue spectral information sensitive to the color of iron hydroxides (i.e., rust) in water. After analyzing a subset of streams, they found that some turned rusty around 2018 and stayed that way, while others had periods of rusting and then returned to being clear.

One stream that underwent a sudden change is the Agashashok River in Noatak National Preserve (above). In 2019, a jump in redness values appeared in Landsat data along this waterway. Ground and aerial surveys the same year found an orange section of the river several kilometers long, and vegetation around nearby groundwater seeps and springs appeared blackened. “The Landsat archive has proved uniquely useful for investigating the historical onset of rusting rivers where creeks and rivers are sufficiently large,” Poulin said.

Having gained a better picture of the extent and timing of the phenomenon, the researchers want to focus on the conditions driving the orange color’s onset and the yearly and seasonal changes. A deep snowpack may play a role some years, for example, by insulating the soil from cold winter temperatures and enabling permafrost thaw earlier in the summer. In addition, periods of higher streamflow throughout the year can dilute the discoloration. The team is planning a geophysical survey along a hillslope where acidic groundwater is discharging to the surface to investigate the subsurface geology, hydrology, and permafrost.

Further, they seek to quantify the effects on water quality and aquatic ecosystems. Communities rely on these river systems for drinking water and subsistence fisheries, and a decrease in stream biodiversity has already been documented in some locations coincident with water turning orange. The researchers now are looking deeper into the patterns of toxicity over time and space, such as where rusting rivers overlap with known spawning areas for migratory fish.

“The rusting river phenomenon is a good example of an unforeseen consequence of permafrost thaw in the Arctic,” Poulin said. “Further, it’s consistent with the emergence of acid rock drainage following cryosphere loss across Earth.”

NASA Earth Observatory images by Michala Garrison, using stream location data from O’Donnell, J.A., et al., and Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.

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References & Resources

• NASA Earth Observatory (2024, January 16) Rusting Rivers. Accessed July 9, 2026.
• O’Donnell, J. A., et al. (2025) Rusting Rivers: Assessing the Causes and Consequences in Alaska and Across the Arctic. Arctic Report Card 2025.
• O’Donnell, J. A., et al. (2024) Metal mobilization from thawing permafrost to aquatic ecosystems is driving rusting of Arctic streams. Communications Earth & Environment, 5, 268.
• U.S. Geological Survey (2026, February 27) The Rusting of Arctic Rivers: Freshwater Ecosystems Respond to Rapidly Uptaking Metals. Accessed July 9, 2026.

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Cyanobacteria blooms turned Blue Mesa Reservoir green from September through November 2021, when water levels were among the lowest on record. The OLI (Operational Land Imager) on Landsat 8 captured this image (right) of a bloom on November 17, 2021, when the water was near its lowest level; the left image shows the same area on November 15, 2017, when water levels were closer to normal.

The summers of 2021 and 2022 were tough seasons for Colorado’s Blue Mesa Reservoir. A severe drought gripped much of the western U.S., prompting emergency water releases that brought the reservoir to its lowest level since 1984. Marinas and boat ramps closed, remnants of a ghost town emerged from the muck, and parts of the reservoir turned greenish and swirled with toxic cyanobacteria blooms.

Research conducted by scientists at the U.S. Geological Survey and the National Park Service analyzed decades of Blue Mesa Reservoir data and found a connection between low water levels, warm water temperatures, and harmful blooms.

“Algal blooms were more common when water levels were below 7,470 feet and water temperatures were above approximately 19.5 degrees Celsius (67.1 degrees Fahrenheit),” said Tyler King, a research hydrologist with U.S. Geological Survey. Water levels that low are relatively common and have occurred every few years in recent decades.  

While some cyanobacteria, also called blue-green algae, are always present in the reservoir in small numbers, problems occur when certain types proliferate. Aphanizomenon, Dolichospermum, and Woronichinia, for instance, thrive when the reservoir’s waters become warm and stagnant, releasing a toxin called microcystin that can cause skin and eye irritation, respiratory problems, and liver damage. Children and pets are particularly vulnerable to microcystin poisoning because of their size and tendency to ingest more water than adults.

King and colleagues analyzed in situ water samples and satellite observations from the European Space Agency’s Sentinel-2 mission and the NASA/U.S. Geological Survey Landsat satellites. A Sentinel-2 sensor that detects the light-harvesting pigment chlorophyll was particularly useful for mapping the blooms, while Landsat sensors were used to map water temperatures over time.

The National Park Service and U.S. Geological Survey launched the project in 2021 after anecdotal reports and water sampling suggested elevated cyanobacteria concentrations, King said. The scientists collected water samples but also turned to historical records and satellite data—”like a time machine,” he said—to examine conditions before regular water sampling had begun. Their analysis included satellite records of chlorophyll levels that extended back to 2016 and temperature records that reached back to 2000. The research team also studied in situ data on water levels dating to the 1970s.

The satellite data showed that blooms typically start in the eastern end of the reservoir, an area known as Iola Basin. The basin, where the Gunnison River flows into the reservoir, is the shallowest part of the reservoir. Occasionally, the satellite data showed, blooms spread westward into other parts of the reservoir, sometimes moving about two-thirds of the way across. However, concentrations of toxins rarely reached levels that posed health concerns beyond Iola Basin.

The same dynamics that caused challenges for Blue Mesa in 2021 and 2022 are present in 2026, said King. Drought again plagues much of the western U.S., the mountains hold little snow, and water levels in Blue Mesa are low. On June 27, 2026, the reservoir stored about 43 percent of the water it typically does on that date, the lowest value observed for that day in the past 30 years. Water levels are expected to continue dropping until October, according to U.S. Bureau of Reclamation projections. 

If cyanobacteria blooms emerge in 2026, the researchers expect that satellites will help scientists track them. The researchers use the U.S. Geological Survey’s WaterMAP (Water Monitoring Above the Planet) tool to monitor for potential bloom conditions within hours of satellite overpasses. NASA’s STREAM (Satellite-based Tool for Rapid Evaluation of Aquatic Environments) project also uses data from Landsat and Sentinel-2 to map potential blooms within hours of a satellite overpass, and the multi-agency CyAN (Cyanobacteria Assessment Network) project collects daily data from other satellites to map blooms in larger water bodies.

“It’s amazing that we can use satellites to map the impacts of microscopic organisms from almost 500 miles away,” King said. Yet it will still be crucial to get people out on the water taking samples and directly testing for toxins, he emphasized. “The satellites aren’t definitive,” he added. “They can tell us where there might be a problem, but toxins often aren’t present until the later stages of a bloom.”

NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey. Photos by Katie Walton-Day (USGS) and Nicole Gibney (NPS). Story by Adam Voiland.

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References & Resources

• Aspen Journalism (2026, January 9) Low reservoir levels main cause of toxic algae in Blue Mesa. Accessed July 1, 2026.
• Aspen Journalism (2021, September 4) Blue Mesa Reservoir releases to prop up Lake Powell impacting recreation. Accessed July 1, 2026.
• CPR News (2021, September 3) Drought-Hit Blue Mesa Reservoir Losing 8 Feet Of Water To Save Lake Powell. Accessed July 1, 2026.
• The Colorado Sun (2023, June 16) Side-by-side photos show how much Blue Mesa Reservoir’s water levels have risen thanks to this winter’s snow. Accessed July 1, 2026.
• The Colorado Sun (2022, September 22) At Colorado’s largest reservoir, one national park scientist shifts her focus to toxic algae. Accessed July 1, 2026.
• Environmental Protection Agency (2026, January 5) Cyanotoxins (microcystin). Accessed May 28, 2026.
• King, T. V.,  et al. (2025) Remote Sensing of Chlorophyll a and Temperature to Support Algal Bloom Monitoring in Blue Mesa Reservoir, Colorado. JAWRA Journal of the American Water Resources Association, 61(4), e70038. 
• National Park Service (2026) Reservoir Levels. Accessed July 1, 2026.
• U.S. Bureau of Reclamation (2026) Blue Mesa Reservoir. Accessed July 1, 2026.
• U.S. Bureau of Reclamation (2026) Reservoir Storage Dashboard. Accessed July 1, 2026.
• University of Colorado Boulder (2026, January 26) Low reservoir levels main cause of toxic algae in Blue Mesa. Accessed May 28, 2026.
• U.S. Drought Monitor (2026, May 28) Colorado. Accessed July 1, 2026.
• Walton-Day, K., et al. (2025) Environmental Characterization of Blue Mesa Reservoir and Potential Causes of and Management Strategies for Harmful Algal Blooms, 1970 through 2023, Curecanti National Recreation Area, Colorado. U.S. Geological Survey Scientific Investigations Report, 2025–5109.

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