We used a time series of Secchi disk values retrieved from Landsat 5 images to study temporal and spatial patterns of water quality across gravel pit ponds located in Madrid, Spain from 1984 to 2009. There is a seasonal behavior in the water quality, with higher values of Secchi disks in autumn and winter (December--February) and lower values in summer (July--August), which can be explained by the relationship between Secchi disk values and temperature and solar radiation. We found that the 1994 administrative declaration of the regional park has had a positive impact on the water quality. The trophic state of the studied pit ponds has slowly improved, though the ponds have not reached the oligotrophic state. [ABSTRACT FROM AUTHOR]