The Graham catchment is dominated by native forest (nearly 80%) with a further 15% in scrub. Some pastoral farming occurs in the lower reaches covering approximately 2% of the catchment area. Sandstone is the dominant geology with small amounts of flood plain gravels in the lower reaches. Rainfall is moderate to high and is dominated by north-westerly air flow patterns. Native biodiversity is high with a wide range of native fish species present in the catchment.