The Whanganui River could be New Zealand's largest inanga spawning site.
Horizons Regional Council staff have pinpointed sites where inanga have laid eggs along the Whanganui River during a hands-on hunt recently.
Inanga are the most numerous of the five species that make up whitebait.
Horizons senior environmental scientist for water quality Logan Brown said their spawning, or egg laying, site at Whanganui is nearly 13km long and larger than the site discovered at Whirokino on the Manawatu River which was previously considered the largest known spawning site in New Zealand.
Mr Brown says that to ensure whitebait remain available for people to catch, it's important to identify those areas that are used for spawning as they're vital in providing future generations of fish.