The relation between (inter)national programs aiming at nutrient load reduc
tion and changes in eutrophication has been studied for 231 Dutch lakes ove
r the period 1980-1996. Trends in total-phosphorus (P) and total-nitrogen (
N) were negative, as determined by analysis of both individual lakes and th
e complete data set. The relative trends in the nutrient concentrations as
well as in the N/P ratio correspond with the significantly reduced P emissi
on and the limited reduction of N emission in The Netherlands since the beg
inning of the 1980s. Negative trends in chlorophyll-a and positive trends i
n Secchi-disc transparency may be partly explained by reduced nutrient conc
entrations. Perspectives for the nearby future are discussed. Lake characte
ristics had only a minor impact on the trends. The improvement of the water
quality was found for all subsets of average depth, surface area, hydrauli
c retention time and soil type. Furthermore, the effect of restoration meas
ures and meteorological conditions on the trends were studied. Biomanipulat
ion resulted in an additional improvement of several water quality variable
s compared to lakes that were only subject to (inter)national programs on n
utrient load reduction. Specific measures resulting in additional P load re
duction resulted only in lowered P concentrations. Severe winters resulted
in lower chlorophyll-a concentrations in the following summer and dry condi
tions in spring were favourable for all eutrophication variables in the fol
lowing summer.