Christchurch was once a mosaic of wetlands and small waterways formed by the past actions of the Waimakariri River and its underground aquifers. Prior to the wetlands being drained and the urbanisation of Christchurch city, the habitat the river passed through was abundant in flax (harakeke), toetoe, raupo, tutu and ferns and was dotted with ti kouka (cabbage tree). The river corridor was low-lying and very wet. The only remnant of the marsh that remains today is the Beckenham Ponds, formed from natural springs in Beckenham Park.
Prior to extensive modification for urban and industrial development, many aquatic species would have flourished in Christchurch waterways. Tuna (longfin and shortfin eels), freshwater fish such as bullies, inanga, kowaro (Canterbury mudfish), kākahi (mussels), kōura (crayfish), and estuarine fish such as kanakana (lamprey) and pātiki (flounder) were important food sources for Maori. They are still found in the river, but is likely in much smaller numbers than pre-European settlement.
Barriers to fish migration - a usual part of our native fish breeding cycle - all contribute to declining fish populations. Weirs, confinement of waterways (especially tributaries) into pipes or boxed culverts, and specifically in the Ōpāwaho Heathcote River, the construction of the tidal barrage in Woolston, are serious impediments fish passage and a healthy waterway.