This paper reports observations on the effects of oil population on mangroves in Botany Bay. Observations of the short-term effects (large-scale seedling kill and defoliation of all oiled leaves on bushes; death of some pneumatophores) of one oil contamination incident are reported first. Secondly, it is suggested that the correlation between oil contamination and die-back of mature mangrove trees indicates a long-term effect of oil population which has not previously been reported in Australia. If mangroves are to be retained in the Towra Point/ Quibray Bay area they must be protected from contamination by oil. Prevention of oil spills, and measures for the collection and containment when they do occur, need much improvement.