Your Landseer has the ability to dive and retrieve things under water. Many dogs refuse to do such an activity but Landseers excel at the sport. You will need to teach your dog to retrieve heavy items on land and once the pooch has mastered the task it is time to throw the item directly into the water and encourage them to dive for it. Most Landseers will not even hesitate but will immediately jump into the water's depths.
Landseers are natural born swimmers. They adore the water. Every muscle in their body and their feet are adapted to make them powerful swimmers. Why not share the activity together? You can swim side by side in a lake, pond, river, or at home in the pool. Your Landseer will truly love the experience and it is good exercise for both of you.