Ho (= lake) Tay is located in the western part of Hanoi City, and is the largest of the lakes of the Red River (Song Koi R.) delta. It is horseshoe- shaped and may be divided into two parts; the upper part is small and shallow with a surface area of 176 ha and the lower part is longer and deeper (237 ha). Its surface area has been progressively reduced, from 466 ha in 1960 to 413 ha in 1992, owing to the filling by human population encroaching the lake.

The lake had originally been a segment of the course of the Red River, but is now a semi-closed water body with only small inflow- and outflow-channels. It receives a daily amount of wastewater of about 10,000 m3 from surrounding urban areas. The increase of population around the lake resulted in moderate eutrophication. The growth of water hyacinth extensively covers the southern shore side of the lake, causing a serious trouble. Mud deposits 50 - 80 cm in thickness are found on the flat lake bottom.

Ho Tay provides the highest scenic spot in Hanoi. Lake-front open spaces are being developed for various recreational activities including fishing, boating and sightseeing for the citizens as well as for tourists (Q, 6).