(Wilcock & Nagels 2001; Wilding et al. 2012).
Oxygen is essential for the process of respiration
and is therefore a limiting substance to most
aquatic organisms. Consequently, the dissolved
oxygen concentration of water is a key control of
habitat quality and a critical measure of stream
health.
Lowland rivers, including estuaries and tidal
reaches, are important habitats for fish. They also
act as critical migratory pathways to and from
upstream habitats for diadromous fish species
that undertake obligatory, regular and seasonally
timedmigrations between the sea and fresh water
to complete their life cycles (McDowall 1990).
Fish species such as inanga (Galaxias maculatus)
and smelt (Retropinna retropinna) also utilise lowland
river habitats for spawning.Maintenance of
suitable conditions in lowland rivers for both fish
passage and resident species is therefore crucial
to ensuring the long-term sustainability of fish
populations. Achieving this will be a significant