How can i get rid of pond dill weed?

We have a small spring fed pond. We just dredged and completely emptied the pond and we are still getting dill weed growing. From a distance you may think the pond has algae growing but up close you can see this green weed with wispy roots on top of the water. It will overtake the pond (again_ if we don't get it under control. We want to put goldfish in the pond. Please advise...thank you!!