An unusual stench emanated from the coastal waters of southwest coast of India during September 2004 associated with an algal bloom. Water samples collected from 14 stations from the affected area after three weeks of the event, revealed that phytoplankton were dominated by holococcolithophorids (max 27 x 10 sup(6) cells l sup(-1)) in the coastal stations in comparison with the offshore stations (max 8000 cells l sup(-1)), which contained mainly diatoms. Slightly low oxygen concentration (81-191 Mu M) associated with relatively lower temperature and high nutrients indicated the prevalence of weak upwelling in the region. Chlorophyll a to phaeopigments ratio at the coastal stations indicated that the bloom was in the degrading phase. Resultant microbial activities perhaps led to higher ammonia concentration in the study region. The holococcolithophorids seem to be uncommon to this region, but upon availability of right conditions, presumably temperature and nutrients formed massive bloom and consequently a stench affecting coastal population.