The Nelson fish survey in 2004/5 found few Koaro in the upper Brook, which led to fish passage improvements being made to the Nile St culvert and Manuka Ford.
A recent fish survey of the Brook River by Council, Wildlife & Fish Services and Friends of the Maitai found significant numbers of juvenile and adult koaro fish at the Waimarama Brook Sanctuary. The range in size of fish indicates good recruitment and that the Brook fish passage measures have contributed to this success. Koaro prefer fast flowing riffles with native bush cover – they have an amazing climbing ability, so can be found upstream of waterfalls and high up catchments.