Photos taken on April 15, 2016, show a reservoir on Panshui River covered in water lettuces (Pistia) in Qionghai, south China’s Hainan province. During spring and summer, the water lettuce would grow wildly, blanketing not only the reservoir, but also a 1-kilometer distance of river. When the river’s water level rises during the rainy season, the water lettuces would flow downstream, blocking the Jiaji Hydropower Station and posing potential danger to the dam as well as the power station.

The local government has organized clean-outs, but the water lettuces always mange to outgrow human intervention, giving headache to the local authorities.