Several European cooperation projects are underway as part of the China-Europe Water Platform (CEWP).

One of these projects, led by the University of Évora (Portugal), required the mobilisation of European experts to carry out an initial survey of the Nanxi river basin. Christian Chauvin (INRAE Bordeaux) was invited by the Chinese authorities to take part in this expert mission, which was followed by several other study and exchange missions, and by the visit of Prof. Jianhua LI from the University of Shanghai to Bordeaux-Gazinet.

The Nanxi is a river that drains a relatively unspoilt area of outstanding scenic, tourist and cultural interest, which was designated a National Park in 1988 and is a UNESCO World Heritage Site. It is the last major tributary of the River Ou, on the left bank of its estuary at Wenzhou. Its downstream section is subject to tidal action. A major dam has been built at Gaopucun to supply drinking water to a region of the basin.

This dam now forms the limit of the tidal zone (3 to 4 m tidal range).

A reservoir has been built in the upstream part of the basin, holding back a large part of the low-water flow.

A project for a second reservoir is under study. The conclusions of the group of experts are awaited to guide the decision on the second reservoir project and on a programme for the Nanxi.

The main issues encountered on the Nanxi concern :

• general aspects of ecological degradation linked to the creation of the dam downstream and the reservoir upstream. The problems identified on site and discussed relate to eutrophication (algae growth) and morphodynamic characteristics (reduction in flows and speeds, sinking of the bed, modification of substrates);

• the virtual disappearance of Ayu (Plecoglossus altivelis) populations. This migratory fish is emblematic of several rivers in China, including the Nanxi. Populations have collapsed, and there is a lack of data on whether they are still effective and viable. This problem is the main challenge of the restoration programme.

Generally speaking, China has high expectations of scientific and technical collaboration in the environmental field, and more specifically in the water sector. Numerous initiatives have been undertaken to preserve or restore aquatic environments, but there is a lack of basic knowledge, experience and methodology.

Of course, there is still a strong antagonism between development (use of water for hydroelectricity production, drinking water supply, irrigation) and preservation as aquatic environments, but the will of the leaders seems to be effective in considering these environmental issues as important.