The diagnosis of drowning is one of the most difficult in forensic pathology. Diatom analysis has been proposed to provide supportive evidence of drowning but the reliability and applicability of quantitative and qualitative diatom analysis in the diagnosis of drowning is still disputed in the literature. In order to further examine such cases, the authors report the development of a water monitoring system based on algae performed each month at three aquatic locations where drowning victims are frequently found. Water samples and stones were taken from the surface and from the bed of the river. This protocol was performed during 1993 with analyses both on water samples and human tissue samples (30 bodies). The diatom profile of the drowning sites was compared with the tissue analysis. The extraction of diatoms from the tissues was performed with an enzymatic digestion method using Proteinase K. Results indicate that the monitoring of river diatom populations is an accurate method of generating profiles of the river flora, which can then be compared with the diatom genera found in tissues.