Hello michelle6308,
One option that you may try exploring would be the "Water Fitness" workout type.
If it's not already to the main list in the Workout app on the Apple Watch, try the following steps from the "Add a workout" section here: Workout types on Apple Watch - Apple Support
On your Apple Watch, open the Workout app.
Scroll down and tap Add Workout.
Tap the desired workout.
The page will also help to note the following, "Choose Other when you can't find a matching workout type. In all workouts, the Heart Rate and Motion sensors work together to give you accurate credit. When you use Other, or any workout type available in the Add Workout section, you earn the credit equivalent of a brisk walk when these sensor readings are unavailable."
Cheers.