Limosella aquatica L., a species occurring along riverbanks, has been found rarely in other parts of our country. In the dunes near Zandvoort (in the environment of Haarlem) it was collected in 1835, that is before the beginning of the water catchment for the water supply of Amsterdam. In 1963 the species was found again in this dune area where recharging is accomplished by the supply of water from the river Lek since 1957.