A three-month fishing ban has been imposed again this year along a section of the Irtysh River in Northwest China's Xinjiang Uygur autonomous region in an attempt to protect endangered species of fish.

The ban, which covers 633 kilometers, has been applied each year since 2005, fishery officers said.

"We chose to ensure the ban is in place during April and May because fish in the river migrate along it from Kazakhstan on their way to spawning in the Altay prefecture in Xinjiang and we need to allow time for the young fish to grow," said Zhu Xinying, deputy director of Altay aquatic products bureau.

Fishing also has been banned in other bodies of water in the region. A four-month ban on the Ili River began in February and a 112-day ban on Bosten Lake in Kuerle, China's largest inland freshwater lake, started in March.

The Irtysh River is China's only waterway that ultimately empties into the Arctic Ocean and is home to more than 30 types of rare cold-water fish, including the Siberian sturgeon, Alaska grayling, taimen, cod and pike.

People in the area talk about having been able to easily fish for food in the river up to the 1950s and say you could even scoop out fish by hand.

By the late 1990s, fish in the river became increasingly rare because of the deteriorating environment and overfishing. The worsening natural environment made it very difficult for fish to migrate along the full length of the river.

In the early 1990s, the Irtysh was still producing more than 500 tons of fish a year but the amount fell to 70 tons in 1999 and several types of fish disappeared.

The fishing bans in the past six years have helped the numbers build back up.

"I can say that the number of rare fish in the river has increased to some extent," Zhu said. For example, there were almost no indigenous carp or pike in 2000 but they can now be found in the middle reaches of the river, he said.

Li Zhenjiang, who has lived along the river for nearly 40 years, said people used to live on boats and fish for a living on the river.

"Some of us are making a living from aquaculture now because it's much better paid than fishing," Li said. "To be frank, I have not seen a 'professional' fisherman for almost 20 years."

Zhu said the fishing bans mean there are now no fishing companies in Altay and the number of fishermen living there has fallen to fewer than 100.

"They work seasonally, usually from July to September," Zhu said. "Because the river is covered with ice for almost five months of the year, they cannot make a living from fishing alone."

Fishery authorities have set up five facilities to encourage fish reproduction in Altay in an effort to save rare species. Last year, 30 million indigenous young fish were released.

An official surnamed Wu from the Xinjiang aquatic products bureau said: "In addition to the fishing ban, we have put great effort into enhancing the fishery resource. Every year, a staggering number of young fish are released into Xinjiang's waterways to preserve the area's biodiversity."