Nitella hyalina has always been very rare in the Netherlands. Two records in the province of Friesland are of old date. The most recent record in northwestern Overijssel dates from 1969. It is now only known to survive in the border area of Utrecht and Noord-Holland. Although it is still present at two sites in the Naardermeer, it is seriously threatened by increase in water turbidity. Data on all known localities, ecology and phytosociology are presented. [Article 4 in this series has been published in Gorteria 19 (1993): 88—94.]