The possibilities to use different types of satellite data to detect and monitor algae blooms is investigated in this study. Two cases are presented, both during extensive algae blooms in the Baltic Sea at times when data from several satellite sensors are available. In the first case on July 15 1997, data from four different sensors, including radar data, were acquired within a time frame of two hours. In the second study from the end-of-July 1999, the acquired data set stretches over 5 consecutive days. The total (possible) number of satellite scenes from the second period is more than 30. In the second case-study ocean colour data were available, a data type unfortunately lacking in the first study. The results of the two studies, preliminary for the second case, show that the combination of various satellite sensors not only provides a better coverage in space and time of an algae bloom, but also yields more information about the biological and oceanic characteristics of the sea surface.