Most rivers experience some form of disturbance from agriculture, urbanisation, exotic species or altered flow regimes. In an effort to remediate and assess these impacts, monitoring is undertaken so impacts can be understood and managed. Biological monitoring using macroinvertebrates is a popular method of aquatic biomonitoring because it allows detection of intermittent pollution sources in rivers and reflects how anthropogenic changes directly impact on aquatic communities.

Rapid bioassessment approaches are the most commonly used approach for stream monitoring and are used to measure against biological targets set in policy in the state of Victoria however results do not diagnose specific impacts in a stream. A field based microcosm approach which isolates the effect of sediment quality on macroinvertebrates can characterise factors involved in impairment of aquatic communities and can be a useful addition to current rapid bioassessment protocol. This study investigated the condition of the Yarra River and one site in Brushy Creek (Victoria, Australia) by using two methods; a rapid bio-assessment approach to examine overall stream condition and a field based microcosm approach to isolate the effect of sediment quality on macroinvertebrates. Rapid bio-assessment revealed a gradual deterioration in stream condition from upstream to downstream in the Yarra Catchment and that the Brushy Creek site was in poor condition.

The microcosm approach indicated this deterioration in the middle Yarra may be habitat related as macroinvertebrate assemblages in the microcosms did not significantly vary from those upstream. Pollution, particularly heavy metals, in the lower Yarra are likely to contribute to poor stream condition and nutrient pollution was likely to impact the condition of the Brushy Creek site. This study demonstrated that rapid bio-assessment methods used in conjunction with the microcosm approach can assist in characterising factors involved in impairment of aquatic communities from urban streams and rivers.