A common practice in tropical mangrove forests is to widen, deepen or extend the natural channels, or create new channels, in order to increase drainage to limit mosquito breeding habitats. Such excavations were made around 1984 in the upper shore regions of a forest near Darwin in northern Australia. To determine whether changes near the channels appeared to be affecting the mangroves, we measured the survival of experimentally planted seedlings, vegetation structure and a set of environmental variables at several distances from the channels. We focused primarily on Ceriops australis, the most common species. Surface and sub-surface (30 cm) soil salinity, pH and moisture showed no consistent pattern with distance from channels but measurements before and after spring tides showed significantly greater changes in these soil parameters in the surface than in the sub-surface. The survival of planted C. australis seedlings was lower in the forests immediately adjacent to the channels than in forests further away. The growth of the seedlings, however, did not depend on location. Total basal area increased with distance from channels. The forests adjacent to some channels had a greater proportion of Lumnitzera racemosa and Avicennia marina. Although no consistent patterns were evident in soil variables, some patterns in the vegetation, and poorer survival of the seedlings, suggest that the channels might be negatively impacting C. australis. If this was the case, the effects on the forest were, however, relatively minor and apparently similar to those of natural channels.