The island of Montreal is part of an archipelago at the confluence of the Ottawa and St. Lawrence Rivers. The mixing of waters from two watersheds, the diversity of channel profiles, substrata, and natural riparian communities, and the great length of shoreline give the area a marked biotic richness and high rate of primary productivity. Longstanding public concern over deteriorating water quality and increasing flood hazard has prompted a comprehensive evaluation of the area's aquatic resources by the provincial government. However, these studies have tended to focus on large scale engineering problems and proposals. Urban expansion and the associate pressures on waterfront land have had a persistent and marked effect on the riparian ecosystem. The loss of upland nesting sites, for example, has rendered much of the area sterile to several duck species. The effects on the aquatic community are less clear. This study was undertaken to determine the effects of shorezone development on the communities of aquatic macrophytes in adjacent areas. It entailed the study of 24 paired sites, one site in each pair being off developed shore, the other site being off nearby natural shore. Twenty-two macrophyte species were recorded in all, withVallisneria americana, Elodea canadensis, andCeratophyllum demersumbeing by far the most abundant. Samples taken off natural sites were significantly higher in average species richness and average biomass values than those taken off developed shore. Differences in profile, substratum, and water quality were assessed as possible causes and it is concluded that changes in depth and perhaps the removal of natural substratum are most likely to have been significant factors. The consequences of the observed changes in terms of habitat utility for aquatic fauna are discussed briefly.