The rare Eurasian otter species has been frequently spotted at the headwaters of both China's Yangtze and Lancang (Mekong) rivers, a sign of environmental improvement in the areas.

In Zadoi County and Jiegu Town of Yushu Tibetan Autonomous Prefecture, Qinghai Province, located at the heads of the Lancang and the Yangtze respectively, images of Eurasian otters have been caught by infrared and normal cameras several times in 2017, said the Qumarleb office under the Sanjiangyuan national park administration bureau.

Local inspectors recently captured clear pictures of otters catching fish at the Yangtze head stream, according to the office.

"The Eurasian otters are at the top of the food chain. They eat a large quantity of fish, live in deep water areas, and have high requirements for water quality and river environments," said Xiao Linyun, an expert with Peking University.

"The situation of the animal can be a reflection of the health conditions of the rivers," he said. "The appearance of the otters in the area shows that on the one hand, people are posing less threats to the animal, and on the other, the ecological systems of the rivers are healthy."

By analyzing the images and videos of the otters, scientists believe that there are at least three otter families and two adult male otters living in the areas.

The river heads of the Yangtze and Lancang are part of Sanjiangyuan, home to the headwaters of the Yangtze, Yellow and Lancang rivers. With a fragile ecosystem, Sanjiangyuan has been dubbed "Asia's water tower."

The environment in the area has kept improving in recent years thanks to intensified protection efforts.

China named Sanjiangyuan a nature reserve in 2005. The country's first national park in the Sanjiangyuan area will open in 2020.