There is an algal bloom in a lake in a populated area. As the leading scientist for the water department, what is the most important thing to do, based on scientific evidence about such blooms?

It is important to detect and characterize first the algal species by obtaining water samples from the lake. This is a critical and very important step for prevention, control and mitigation of algal blooms. There a number of methods for this such us microscopic methods, molecular probes and remote sensing techniques.