Introduction
Reports describing the quality of New Zealand’s
fresh waters have indicated a decline in water quality,
and strong relationships between the degree
of agricultural development within a catchment,
lowered water quality, and reduced biodiversity
of stream fauna (Quinn & Hickey 1990; Quinn
et al. 1997; Hamill&McBride 2003; Larned et al.
2004; Wilcock et al. 2009). Typical pressures include
elevated nutrient and sediment loads, loss
of riparian shading, increasedwater temperatures,
low dissolved oxygen, excessive growth of aquatic
macrophytes and loss of physical habitat diversity
(Wilcock et al. 1999; Larned et al. 2004). Lowland
waterways are particularly vulnerable, being subject
to multiple stressors and the cumulative
effects of upstream pressures.
There is increasing evidence to suggest that in
some areas, dissolved oxygen concentrations in
lowland streams and rivers are falling below the
recognised lethal thresholds for some fish species