What eDNA can tell you about your waterway
Environmental DNA (eDNA) is genetic material that fish and other animals shed into the environment through skin cells, mucus, waste and gametes. By detecting these traces of DNA, eDNA can provide a picture of the fish community present in a waterway without the need to capture fish.
For landowners, community groups and iwi, eDNA is a low‑impact, non-technical method to build a picture of the fish community. It's especially good at picking up rare, cryptic or elusive species that conventional methods can miss.
What eDNA does well
- Detects a wide range of species from a single water sample
- Works in places where electric fishing or netting is difficult
- Reduces disturbance to sensitive species and habitats
- Provides a snapshot of the fish community at the reach scale
What to keep in mind
eDNA tells you a species could be present and complements physical capture surveys. However, eDNA cannot currently confirm how many fish are present or the size range of fish species.
Water flow can carry DNA downstream, so a detection reflects the upstream community and not just the exact spot sampled.
Sampling design matters: number of replicates, timing, and stream conditions all affect what you'll detect.
Field protocols
Our national guidelines set out how to plan a sample, avoid contamination, and interpret results in a consistent way across Aotearoa. They cover everything from when to sample, where in the stream to sample, and what to record on‑site.
Download: Environmental DNA guidelines and field protocols for lotic systems [PDF 5 MB]
Understanding replicate numbers and the eFIBI
Six replicates is the standard for eDNA fish surveys in New Zealand because it reliably detects around 90% of the species eDNA can pick up at a site (Smith et al. 2024).
The number of replicates is also important when calculating the eDNA Fish Index of Biotic Integrity (eFIBI), a metric that uses the fish community detected by eDNA to assess stream condition and assign sites to ecological health bands.
But six replicates isn't always necessary, and for some questions fewer will do. Our follow‑up report explains when a lighter sampling design is defensible, and when six replicates should be retained (for example, when reporting against the NPSFM, monitoring rare or invasive species, or working in larger or more complex streams).
