The estuarzes of :the Delta, area in the S.W.-Ne~he~lands, which according to the Delta Plan havel to be closed, willq~ ~filled with fresh water derived from the rivers Rhine and Meuse. Therefor~ ft'is to be exp ecte.d! ithat at ; l as,,: p art .of the freshw-ate= new lakes w~ll :be derived from the river fauna. As there exists~no recent information concerning the fauna of these increasingly more po'iluted rivers and becaUse the Haringv~iet estuary Was ~closed on ~6vembe~ 2nd, 1970, a s~uapllhg"/programm was executed from'25 thrdugh:29.1,~6tiobgri~'|971 on the fauna ~f the river Waal, the~ main branch of the Rhiaer an&af the river Meus e. The fish fauna was isampled by means of a shrimp ~ra~#l with a width of-3 m and a mesh-size 0f I cm; th& benthic fauna with an oyster dredge with a width of 1 m and a Van Veen grab sampling an area of.O.l m 2. The grab samples were sieved through an I ~ sieve and sorted in the laboratory. The fishes caught were identifie d aboard by Messr. P.. de Koeijer and A.J:.J. Sandee and the first author; the benthic: animals were ident.ifled. :b~ the second author, except for thel ~aidiwn's which have been identified by Mr. J.G.J. Kuiper (Paris). The samples were obtained after a dry summer characterized ~by a~!on~ period of low river discharges. Therefore, ~w~ter qual~ty was relatively bad at the moment of our sampling. Our catches, :therefore, probably show a good picture of the minimum fauna of the r~vers P~ine :and Meuse. The number of samples is given in Table I.