California's Clear Lake Turns Green With Algae, Visible From Space: NASA

California's largest freshwater lake has become a vibrant emerald due to a massive algae bloom. The bloom's intensity is so extreme that NASA captured it in satellite images taken in mid-May.

The culprit behind the vibrant hue could be cyanobacteria, also known as blue-green algae, along with other types of phytoplankton. Clear Lake, a popular hub for fishing, water sports, and recreation (nicknamed the "bass capital of the west"), stretches over 68 square miles in Northern California, roughly 100 miles north of San Francisco.

Local public health officials have warned visitors, urging them to be aware of the algae blooms. This includes keeping pets away from the water and avoiding areas that appear discoloured, have surface scum, or emit a foul odour, as reported by the Press Democrat newspaper.

"The appearance of cyanobacteria in Clear Lake is not unusual, but it has occurred earlier and in greater abundance than in typical years," the newspaper said.

Current levels of toxins in the water are being tested. The Big Valley Band of Pomo Indians has been monitoring water quality at the lake for the past decade. "This year has the earliest blooms since the Tribal program lakeshore cyanobacteria and cyanotoxin sampling began in 2014," a Clear Lake water quality Facebook page noted.

While archaeological evidence suggests humans have inhabited the area around Clear Lake for a staggering 12,000 years, sediment samples reveal the lake has harboured significant algae populations for a similarly vast period.  However, recent human activity has thrown a wrench into this historical balance.

As reported by NASA, these activities include runoff from nearby farms, vineyards, malfunctioning septic systems, gravel mines, and even an abandoned mercury mine. This unfortunate mix has contributed to declining water quality in Clear Lake.

Scientists worldwide are raising concerns about algae blooms' increasing frequency and toxicity, attributing the trend to factors like global warming and the rise of industrialized agriculture. Clear Lake appears to be another example of this worrying trend.