Ducks are creatures of habit and do not like change. I suspect they will be terrified of the lake. Also, what are you going to do if I am wrong and they love it. They may not come out when you want them too. Will there be people with dogs there? A loose, friendly dog could easily kill a duck with one shake. My opinion is that they would be happier left at home with a pet sitter. However, I once saw a family at a public beach who had their pet Pekin duck and their lab with them. The duck was obviously used to following the family and dog and had been to the beach before. He swam in the ocean for the day with the family and then waddled back to the car with them to go home. He was lone duck though, who was obviously very attached to his family.