The invertebrate communities associated with dense beds of exotic macrophytes were sampled monthly between June 1993 and June 1994 from three sites in Lake Henley, a small artificial lake in the Southern Wairarapa, North Island, New Zealand and from a small stream flowing into the lake. All communities were dominated by either the gastropodPotamopyrgus antipodarumor by oligochaetes. Community composition was similar at sites within the lake monoculture but changed seasonally. These changes appeared to be predominantly a result of seasonal fluctuations in the presence of filamentous algae on the macrophyte beds. Communities sampled from the stream site had a number of taxa in common with the lake communities but were quite distinctive in terms of the relative abundance of these component taxa. The diversity of the lake phytomacrofauna community, although comparable to similar studies in other New Zealand lakes, had a lower proportion of insect taxa perhaps because of the low floral diversity, the lack of depth variation, the absence of a nearby colonising source or the young age of the lake.