Simultaneous acquisition of Landsat TM imagery and sea truth data from sample sites in Himmerfjärden bay on the Swedish east coast was conducted on 10 May 1988, and 7 May 1990. The data were used to develop and verify regression models for the estimation of surface chlorophyll-a concentrations. The case 2 waters studied partly hold suspended sediment concentrations known to complicate the mapping of chlorophyll-a. The disturbing spectral influence from suspended sediment was reduced by using a process based on an existing Landsat TM sediment retrieval algorithm and a priori knowledge about water depths, bottom sediments and river outlets. The results suggest that a ratio of TM bands TMl/(log TM3+1) should be used in waters influenced by terrigenous influx and the earlier suggested ratio of TM bands 1/2 only in ocean waters. The discrimination power indicated a capability to quantify chlorophyll in connection with algae blooms.