A catchment is an area of land where all the water that falls as rain (or snow) drains into a common outlet, such as a river, lake or the sea. It is naturally bounded by higher ground like hills or mountains, which define the area and separate it from other catchments. 

Catchments vary greatly in size, from small areas that drain into a local stream to vast catchments like Kaipara Harbour, that has a land area of c 640,000 hectares, with numerous rivers and streams that drain into the harbour.

When rain falls, gravity causes it to flow downhill. The water moves across the surface of the catchment as runoff, and underground as groundwater, before feeding into streams and rivers.

What happens anywhere within a catchment can impact water quality and quantity downstream. The entire area is interconnected, meaning any activity within the catchment, like land use or pollution, can affect the water in the main river or lake. If chemicals or paint are emptied into a drain, for example, they don’t disappear. Instead, those pollutants flow into streams and rivers within the catchment and eventually will reach lakes or the coast, harming water quality and aquatic life.

To help visualise a catchment, NRC’s Land team was fortunate to have the support of the Whangārei Men’s Shed. Their volunteers, Jon Borrette, Chris Grbin and Andrew Westenburg, worked for several weeks on a beautiful catchment model, with a pump to enable water to be pumped through it, demonstrating the water’s journey. Thank you to Jon, Chris, Andrew, and all the others involved from Whangārei Men’s Shed.

The NRC Land Management team can help with advice for landowners on catchments and how to improve water quality through fencing, native bush regeneration and native planting, and any relevant funding opportunities.

The land team and the catchment model will be at Northland Field Days in Dargaville on 26, 27 and 28 February 2026. Come along for a chat about your property and how NRC might be able to help.

Find out more about land management