Swimming with proper form is effective as a full body exercise and for improving proprioception and movement in and out of the water.
Total Immersion Swimming is a training method for marathon swimming, with a focus on developing proper form to increase distance per stroke.
Notice the smooth, intentional movements.
Swimming with a mindful focus on form will improve strength and mobility body-wide. As form improves, the distance traveled per stroke increases, and swimming starts to feel like flying.
Here are some of the drills I used to learn this swimming technique: