Nonstructural carbohydrate content was examined in Ceratophyllum demersum L., Elodea Canadensis Michx., Myriophyllum exalbescens Fern., Najas flexilis (Willd.) Rostk. & Schmidt, Potamogeton foliosus Raf., P. gramineus L., P. praelongus Wulfen, P. richardsonii (Benn.) Rydb., P. robbinsii Oakes, and P. zosteriformis Fern. at various depths and sites in Shoal Lake. Species tended to show a seasonal maximum in total soluble carbohydrate content during the growing season. Starch and proportions of individual sugars also showed seasonal variation. Sucrose was the predominant sugar in most species. c. demersum was unique in being the only macrophyte containing melibiose, raffinose, and stachyose. Roots contained significantly more soluble carbohydrate than shoots and leaves in M. exalbescens. Starch concentrations generally exceeded levels of soluble carbohydrate. All carbohydrate variables were negatively correlated with water depth in c. demersum, E. canadensis, and P. foliosus. Starch was significantly negatively correlated with time in C. demersum and marginally positively correlated with time in P. zosteriformis. Stepwise multiple regression identified time and pH as significant factors in relationship to carbohydrate content in some species. The first principal component for total soluble carbohydrate in 5 species was significantly correlated with light and depth.