Previous research has suggested thatEuhrychiopsis lecontei, an aquatic weevil native to North America, may act as a biological control for Eurasian watermilfoil. To be able to predict which lakes weevils are likely to be effective in laboratory and field studies were carried out under a range of conditions. In the laboratory, weevils survived and reproduced in water up to 31°C, but not at 34°C. Weevils preferred Eurasian watermilfoil plants with no marl, but ate and laid eggs on marl-covered plants. The weevils preferred plants grown in richer sediment, but did eat and lay eggs on plants grown in poorer sediment After open water releases of weevils in three lakes, weevil populations were established and had a negative impact on Eurasian watermilfoil. We have followed a Eurasian watermilfoil decline from 1990–1995. Plant and weevil abundance have varied over the years; however, Eurasian watermilfoil has never regained its former dominance. Based on these trials, it appears thatE. leconteican survive and cause damage over a range of temperatures and plant conditions. Wider scale introductions would help determine the conditions under which this weevil is successful, and its limitations as a biological control for Eurasian watermilfoil.