Effects of water chemistry and catchment afforestation on benthic invertebrates were investigated in acid brownwater and circumneutral clearwater streams in Westland, South Island, New Zealand. Annual dissolved organic carbon (DOC) budgets calculated for three North Westland wetland catchments (zero, two and five years post-afforestation) showed that forestry development resulted in a reduction of DOC export by up to 24 % and that recovery of DOC dynamics was linked to the time elapsed since the onset of development. The presence of high DOC concentrations in stream water (up to 41 g.m-3) resulted in lowering of pH to about 4.0. These highly acidic waters also contained high concentrations of dissolved aluminium, but only a small proportion (< 80 mg.m -3) was in the toxic labile (inorganic) monomeric form.