Lakes of the midwest are small and heavily impacted by nutrient pollution and sedimentation. Despite the rarity of a high proportion of deepwater aquatic plant species thoroughout the region and their essential ecological role as habitat for invertebrates and fish, little effort has been made to evaluate the potential usefulness of aquatic plants as indicators of biotic integrity. During the spring and summer of 1997 and 1998 we surveyed aquatic plants of the ten lakes of the Valparaiso lakes watershed in Northwest Indiana. The lakes are small with surface area of 1480 acres and a watershed of 2500 acres. The lower lakes are impacted by urbanized/industrialized areas of the City of Valparaiso. Objectives of the study were to: 1) provide comprehensive inventory data on aquatic plant species distribution and abundance in relation to habitat quality 2) to study life-history characteristics of state listed species to determine their critical habitat requirements and evaluate their potential as indicators of ecological stress. 3) To determine the usefulness of aquatic plant data in the assessment of biotic integrity. We identified 105 species of aquatic plants from the lakes with 12 of these being state ranked. One of these species ( Ceratophyllum echinatum ) is a first record for Indiana, Lemna valdiviana is listed as extirpated and Potamogeton vaseyi is the first recorded population of this species in 70 years. The aquatic plant data set indicate lakes in the upper part of the watershed have higher floristic quality, species richness and a lower proportion of invasive species. In the absence of historical data it is difficult to assess whether the absence of state listed species from lakes lower in the watershed is actually due to degraded water quality or competition with exotics although the small size of the watershed is suggestive that it is the latter.

Key words: aquatic plants, biotic integrity, Ceratophyllum, endangered, midwest, Potamogeton