California’s Clear Lake turned cloudy green in NASA image

California’s largest freshwater lake has turned a lurid green thanks to a massive algae bloom, as seen in photos taken from space.

Located about 120 miles north of San Francisco, Clear Lake has long been plagued by significant algae blooms, raising environmental and health concerns.

In images taken by the OLI-2 (Operational Land Imager-2) on the Landsat 9 satellite on May 15, the lake can be seen shining bright green as a result of one of these algae blooms.

Clear Lake has an area of ​​approximately 40 square miles and is the oldest lake in North America at approximately 500,000 years old. It is home to large fish populations and attracts numerous bird species, including ducks, pelicans and bald eagles, making it a popular spot for nature lovers. The lake regularly experiences algae blooms, as the warm water and shallow depths make it an excellent breeding ground for algae.

clear lake of California
An image from space shows Clear Lake in the middle of an algae bloom on May 15, 2024. Such algae can produce toxins that are harmful to humans and animals.

NASA Earth Observatory image by Wanmei Liang, using Landsat data from the US Geological Survey.

Algal blooms in Clear Lake are mainly caused by cyanobacteria, also known as blue-green algae. These single-celled organisms thrive in nutrient-rich environments, especially when phosphorus and nitrogen are abundant.

“These excess nutrients can cause harmful algal blooms (HABs). This is a bust-or-boom scenario where, for example, blue-green algae will multiply and use all available dissolved oxygen,” says Ian Hendy, a senior scientific fellow at the Institute for Marine Sciences from the University of Portsmouth in England, narrated Newsweek.

This is often exacerbated by agricultural runoff and other human activities such as mining and sewage treatment, as these increase the levels of nutrients in the water, leading to more severe and regular algae blooms.

On May 15, the same day the photo was taken, levels of chlorophyll-a, a chemical used by algae and plants to harvest light energy, reached some of the highest levels of the month in Clear Lake waters.

More than 130 species of algae have been found in Clear Lake waters, three of which can be harmful to human health. According to a statement from the NASA Earth Observatory, some algae in Clear Lake can produce toxins, such as microcystin, that pose serious health risks to both humans and wildlife. Microcystin can cause skin irritation, liver damage and even kidney failure when ingested.

Even if these toxins are not present, algae blooms can strip all the oxygen from the water and potentially cause fish and other life to suffocate.

“This process creates very low oxygen levels in the water, making life very dangerous for aquatic organisms such as fish and invertebrates,” Hendy said.

Algal blooms in Clear Lake have significant ecological and recreational impacts, as residents and tourists are advised to avoid water activities such as swimming and fishing due to the potential health risks. The visual impact of the flowers also deters visitors, impacting tourism and the local economy.

Clear Lake is not unique in meeting these challenges; Similar problems have recently been observed in other large bodies of water, such as Lake Winnipeg in Canada and Lake Okeechobee in Florida. Both lakes have experienced severe algae blooms due to a combination of warm temperatures and nutrient-rich runoff.

The situation at Clear Lake highlights the broader environmental problems caused by nutrient pollution and climate change. As water bodies warm and nutrient levels increase, the frequency and severity of algal blooms are expected to increase, requiring concerted efforts to protect water quality and public health.

Do you have a tip about a scientific story that Newsweek should cover? Do you have a question about algae blooms? Let us know at [email protected].