Selecting a lake improvement method can be facilitated by computer simulation of the effects of various alternatives on lake water quality. Dynamic simulation of cause/effect relationships on the most important physical, chemical, and biological processes encountered in a lake allows extrapolation to future conditions on a rational basis. Not all lake processes are understood well enough to be properly modeled. However, features such as temperature stratification, turbidity, nutrient levels, and phytoplankton populations have been simulated successfully. A discussion of types of lake improvement techniques which can be simulated and those which cannot be simulated will be made. Examples of simulations evaluating improvement techniques will be given. Dynamic water quality simulation is an efficient and rational tool to compare quality and cost effectiveness of certain lake improvement techniques.