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The Brokopondo Lake in the interior of Surinam began to form when on 1 February 1964 the dam in the Surinam River near Afobaka was closed. The lake was intended to cover an area of about 150.000 ha and to have a maximal depth of about 47 m.The basin, largely occupied by forest, was not cleared beforehand. During the initial stage the water in the flooded forest was characterised by a very high content of organic matter and the absence of oxygen. As the water level rose, differentiation between a hypolimnion and an epilimnion developed. The oxygen content of the epilimnion was high.During the first three years of its existence the lake attained an area of about 84.000 ha and a maximal depth of 38 m.Within this period eight aquatic plant species became numerous in the lake. Special attention was paid to Eichhornia crassipes and Ceratopteris pteridoides. In April 1966, when the lake covered about 78.000 ha, the former had colonized 53 %, the latter 21 % of this area.Since September 1966 both diminished greatly, Eichhornia as a result of artificial control, Ceratopteris for unknown reasons.Floating pieces of decaying wood became overgrown by a variety of plant species, 27 of which were recorded.Mixed vegetations of water and marsh plants developed, free-floating mats (Eichhornia being the matrix), patches attached to partly submerged tree tops, and belts along the shore. Twentytwo species were observed as constituents of these floating vegetations.