Lake Ypacarai is a shallow and swampy natural lake located some 30 km east of Asuncion, the capital of Paraguay. It has a surface area of approximately 60 km2 and a maximum depth of 3 m. The catchment basin of 833 km2 is largely covered by pastures and crop fields.

There are some 20 inflowing tributaries of various sizes, while only one river, Rio Slado, drains the lake joining the Paraguay River at about 20 km downstream. An extensive area of wetlands with luxuriant growth of emergent and submerged plants develops near the lake's outlet and maintains the lake water level effectively within a narrow range of fluctuation.

Since natural water bodies are particularly valuable for this flat inland country, Lake Ypacarai district offers one of the best sites for tourism and outdoor recreation in Paraguay, with abundant facilities for visitors and summer houses around the lake. The lake water is also used for drinking water supply and irrigation.

The lake has recently suffered from progressive eutrophication owing to the nutrient discharge from surrounding crop fields, livestock farms, residential areas, deforested lands and large-scale land development. An international multi-disciplinary research project has been launched since 1987 by the national government to cope with this problem (Q, 1).