Macroinvertebrate colonisation of perspex multiplate artificial substrates suspended in the Ohinemuri River, New Zealand, was investigated over a 70‐day period. Community development was examined in terms of the colonisation and extinction rates of the MacArthur‐Wilson equilibrium model for island faunas. Although colonisation and extinction rates were equal at 35 days, permanent stability was not attained: the extinction rate and colonisation rate continued to fluctuate as new taxa continued to colonise. This lack of permanency was attributed to changes to the surface of the plates through increases in the accumulation of fine paniculate matter, and to changes in the drifting fauna that affect the pool of potential colonisers. Stream drift was an important source of colonisers, especially in the initial stages of colonisation. Although many members of the New Zealand aquatic fauna have non‐seasonal life cycles, and are present as larvae at all times of year, they may occur seasonally in the drift. Therefore colonisation patterns may differ seasonally. Drift was not the only source of artificial substrate colonisers.