Clarence River sediment survey establishes health baseline

Published: 21 September 2026

More than 200 citizen scientists, First Nations custodians and Southern Cross University researchers have completed the Clarence River catchment's largest community-powered sediment survey. The results are now public and establish a health baseline for this significant waterway.

Across a single weekend in October, 2025, more than 120 samples for the Clarence River Guardians Baseline Sediment Survey were taken from more than 100 sites across 22,600 square kilometres of river and catchment.

Southern Cross University researchers spent months preparing and testing the samples for more than 50 chemical elements, including heavy metals. The results are now live in an interactive map-based dashboard. Investigate them here.

A catchment tested at scale

Months of planning, training and logistics began before collection weekend. Small teams worked from central hubs in Grafton and Tabulam, and coordinated using GPS-enabled smartphones, QR codes and digital mapping apps. Each team received on-line training, sampling kits, maps and instructions, and worked unassisted once in the field.

First Nations custodians helped co-design the survey from project development through to ensuring sample sites were culturally appropriate. Every sediment sample will be returned to its point of collection in the river in an event being planned for 2027 out of respect for Country, the river and Traditional Owners.

Testing found arsenic, chromium, copper, zinc and other metals across the catchment- elements that occur naturally in the region's rocks, soils and sediments.

“When measured against national sediment guidelines, the great majority of sites sit comfortably within the natural background ranges, and that is a good outcome,” said Professor Scott Johnston, project lead at Southern Cross University.

“Only a small handful of sites were above the higher guideline level values, and there's usually a natural explanation like local geology, or the legacy of historic mining in parts of the catchment.” he said.

"The sites with high levels due to past mining appear to be very localised, but it is a reminder that mining-related effects on sediments can be very long-lasting and therefore we need to take proper care of the river in the future.''

Gorge with water — Nymboida Gorge sits within the 22,600 square kilometre Clarence River Catchment. Photo: Professor Scott Johnston

A public record for future testing

Made up of a broad cross-section of community groups, industry and government representatives, the Clarence River Guardians Project formed in 2024. Planned expansions of mining exploration licenses had led to concern about negative impacts on river water quality, river sediment quality and aquatic ecosystem health.

The Project, now including First Nations custodians, Southern Cross University and Lions Club of Clarence (Environmental), is focused on increasing knowledge, care and awareness of, and establishing parameters and scientific information about, Clarence River and its catchment. This includes on-going community-University monitoring of water quality in the Clarence River, which can be viewed online.

“The baseline sediment survey and ongoing water quality testing sets up the Community for future monitoring, and repeat surveys can now be measured against this data. Over time, that comparison will show whether conditions in the catchment are improving, holding steady or changing,” said Professor Johnston.

“We’re establishing a foundation for river care that will outlast this generation.”