In this report the development of a model for simulation of waste water or cooling water dispersal is presented. The model, called MALMAK, is designed to provide information suitable for environmental impact assessments of the initial spreading of plumes around point sources. It works well with the limited information typically available for assessments of discharges to water recipients and does not require detailed monitoring of ambient conditions. The model development described in this report includes an algorithm for predicting the plume width from the momentum of ambient and effluent water, a new model interface and an inbuilt graphic module enabling simulation results to be directly represented in a digital map. The model has also been validated against empirical data and against a more complex hydrodynamic model and was found to give reasonable estimates of effluent concentrations in aquatic environments.