Students stand on the roof of a wooden boat as haze blankets the Musi River while they travel to school in Palembang, on Indonesia's Sumatra island, September 10, 2015. Indonesia is investigating 10 firms over worsening forest fires that have created a blanket of smog over Southeast Asia, threatening them with sanctions if they are found responsible, a government minister said on Tuesday. The thick haze from Indonesia's Sumatra and Kalimantan islands has forced the repeated cancellation of flights in the area and pushed air quality to unhealthy levels in neighbouring Singapore and Malaysia. (Photo by Reuters/Beawiharta)

Elderly women wait for customers as they sell their self-made food products at a street market, with a graffiti depicting Russian President Vladimir Putin on the wall of a house seen in the background, in the town of Kashira, outside Moscow, Russia on October 10, 2017. (Photo by Andrey Volkov/Reuters)

In this June 29, 2016 file photo, boats docked at Central Marine in Stuart, Fla., are surrounded by blue green algae. The 153-mile-long Indian River Lagoon has been plagued by harmful algae blooms. Water quality testing data analyzed by the AP showed the average phosphorous level – a byproduct of fertilizers and human waste that algae thrive on, rose nearly 75 percent between 2000 and 2016. (Photo by Greg Lovett/The Palm Beach Post via AP Photo)

A motorcyclist ferries a pillion rider sitting on goods in Phnom Penh on June 6, 2017. (Photo by Tang Chhin Sothy/AFP Photo)

Seven-year-old Mimi Meade winces from the sting as Dr. Richard Mulvaney inoculates her April 26, 1954 in McClean, Va., with the new Salk polio vaccine. Mrs. John Lucas, a registered nurse, holds Mimi's arm steady as she gets one of the first injections of the countrywide test. (Photo by Harvey Georges/AP Photo)

A woman, covered in coloured powder, takes part in the 2019 Colour Run, a 5 km run around the Luzhniki Olympic Complex, in Moscow, Russia on June 02, 2019. (Photo by Sefa Karacan/Anadolu Agency/Getty Images)

Hidden Britain category winner. Garden Spider by Alan Smith from Reading, Berkshire. (Photo by Alan Smith/British Wildlife Photography Awards/PA Wire Press Association)

Models present creations during the 8ON8 PRESENTED BY GQ China catwalk show at London Fashion Week Mens Spring/Summer 2020 in London, Britain, January 5, 2020. (Photo by Henry Nicholls/Reuters)