Bắc Kạn province

The limited water resources development in the province is managed by the communes through better water management practices (government supported initiatives) such as water users associations both for domestic water use and agricultural operations. The irrigation systems developed, though often of temporary nature, in many communes. The participatory management practices adopted since the 1990s has resulted in a greater realization by the farmers that they can play a positive role in the development of irrigation systems in their region for their own benefit. This system has ensured more efficient water delivery to the fields and is reported to have increased the cropping area by 15% and yield levels by 20%. This has resulted in improved economic and living conditions for the farmers.[4]

Karst limestone formations on the banks of Ba Bể lake

Francois langur

Snub-nosed monkey in the reserve area

Ba Bể Lake located at an altitude of 178 metres (584 ft), in the midst of the Ba Bể National Park has a water spread area of 500 ha bounded within geographic coordinates of (22.233°N 105.566°E / 22.233; 105.566) and (22.5166°N 105.733°W / 22.5166; -105.733). The lake's water stretch is over 8 kilometres (5.0 mi) (from north to south) with a width of 800 metres (2,600 ft)(average). The depth of the lake is from 20–25 metres (66–82 ft) to 35 metres (115 ft). The bed of the lake is uneven with submerged mounts and also limestone islets. The details of the lake have been submitted for UNESCO recognition under the Criteria: (viii)(ix), Category: Natural Submitted by the Ministry of Culture and Information - Government of Vietnam. It is the biggest natural lake in Vietnam, formed in the Chợ Rã-Ba Bể-Chợ Đồn karstic or "Karst" low-lying terrain in the northern midlands. Its formation is attributed to the raising mass formation “from the destruction of South East Asia continental mass at the end of Cambrian era, around 200 million years ago”. As opposed to similar karstic lakes in the world, it retains its full storage all through the year. The Government of Vietnam has also notified the lake as a forest preserve and a techno-economic study was instituted as part of the National Park Conservation programme.[14][15][16]

The lake and its environs have rich biodiversity of flora and fauna. Among the flora recorded are 417 species of trees, several species of orchids and species of medicinal plants; 179 species of phytoplankton belonging to Chlorophyta, Cyanophyta, Bacillariophyta, Euglenophyta, Pyrrophyta and Chrysophyta have been observed in the lake as well. The faunal species recorded are of terrestrial, aquatic and flying varieties. These are 319 species of animals, out which 42 species are recorded in Vietnam’s Red Book with 3 endemic animal species; the endemic species are the gibbon (snub nose), bamboo-thread and red algae.[14][15] 106 species of fish recorded in the lake consist of 61 genera, 17 families and 5 orders.[16]

The three lakes, also called the Slam Pe in the local Tày ethnic language, that form Ba Bể lake are called the Pé Lầm, Pé Lù, and Pé Lèng; all linked as one waterbody. The lake’s central part is contracted while its outer two parts are wider. The lake's hilly catchment drains 3 rivers into the lake, namely, the Tả Han, Nam Cường and Chợ Lèng rivers from south and west and is drained by the Năng River flowing to the north. The lake water is very clear with blue colour, and it is a flowing lake with a velocity maintained by controls at 0.5 metres (1.6 ft)/s. The lake acts as a flood absorption reservoir during the high flow stages of the Năng River when reverse flow occurs from the river into the lake, preventing flooding in the Năng, Gâm and Lô river deltas. The Năng River flows southwards, eventually joining the Lô River in southern Tuyên Quang province, before debouching in the Red River west of Hanoi.[14][15][16]

The narrow central part of the Ba Bể Lake in the dry season.

Ba Bể National Park, established in 1992, covers an area of 100.48 square kilometres (38.80 sq mi), delimited within geographical coordinates of 22°24′19″N 105°36′55″E. It was set up to protect the Ba Bể Lake along with its surrounding limestone and lowland evergreen forests. The South-West valley of Phiabyior Range of the park has mountain peaks with an elevation range of 517–1,525 m.[14] The reserve forest has two main types of forest vegetation namely the limestone and lowland evergreen forests. The limestone forest, the larger of the two types in the reserve has steep limestone slopes with shallow soil cover. The forest species recorded are mostly Burretiodendron hsienmu and Streblus tonkinensis. The other type is the lowland evergreen forest shallow slopes with a thicker mantle of soils. It has a rich ground flora with a higher diversity of tree species.[15]

Park sign near the lake management station

There are 65 mammal species in the park. The prominent ones are Owston's civet (Chrotogale owstoni; globally vulnerable), Francois' leaf monkey (Trachypithecus francoisi) and Tonkin snub-nosed monkey (Rhinopithecus avunculus; globally critically endangered).[15] The other species include Chinese pangolin (Manis pentadactyla), slow loris (Nycticebus coucang), rhesus macaque, stump-tailed macaque, François' langur, Asian black bear, European otter, Asian golden cat, mainland serow, red giant flying squirrel, particolored flying squirrel (Hylopetes alboniger), hairy-footed flying squirrel as well as 27 bat species.[16]

About 330 species of butterfly have been recorded, of which 22 are said to be new.[15] Facilities at the park include an information centre, guest houses, a lake management station, and an ecological research station opened in 2004. The park has 13 villages inhabited by five ethnic groups comprising more than 3,000 people, of which the Tày are the oldest ethnic group (over 2,000 years) and form the majority. The other ethnic groups are Dao, Mong, Nùng and Kinh in descending order by population.[16]

Puong Cave in the Nang River

Puông Cave (Vietnamese: Động Puông) is a large cave in the north of Ba Bể Park through which the Năng River flows. The main cave is up to 50 metres (160 ft) high and about 300 metres (980 ft) long, in limestone formation. The cave is inhabited by a large population of bats which belong to 18 species, out of which three species are identified for plant pollination and scattering seeds.[16]

The "Fairy Pond" is an isolated rock basin filled with clear water that seeps through the surrounding limestone rock. However, the water level in this pond is the same as the Ba Bể Lake. The Dau Dang Waterfall (Vietnamese: Thác Đầu Đẳng) is formed by the Năng River. It consist of a sequence of rapids which stretch over a length of almost 1 kilometre (0.62 mi) as the river flows into Tuyên Quang province.

Widow Island is a small, cone-shaped islet near the centre of the southern part of the lake. According to local legend, the islet was once the home of an old widow who was spared from a flood through divine intervention.[16] Other well known caves include Puông Cave, Nả Poỏng, Ba Cửa Cave, Sơn Dương Cave and the Kim Hỷ nature reserve.