Management of Eurasian watermilfoil (Myriophyllum spicatumL.), which was introduced to British Columbia, Canada, about 1970, incorporates various technologies and approaches. Monitoring of Eurasian watermilfoil since 1972 has required development of phytochemical means to distinguishMyriophyllumtaxa, extensive and often repeated surveys of over 1500 lakes, and establishment of a large herbarium and database. Field survey methods have been used extensively to evaluate control procedures, measure rates of plant population change, document and map the spread of Eurasian watermilfoil and its impacts, and provide data to plan annual management. Survey methods used are described and examples of the results are presented to illustrate the application of field survey data to guide decision making and allocation of resources.