I once had a national level HS athlete that was in the pool March to mid May. She ran 5:02 in her first race having jogged 800 meters once prior to racing over that 10 week off period. This was due primarily to her exceptional focus and effort in the pool, not the workouts I gave her. She did all water running with a vest, no swimming.
I did my best to have workouts mirroring somewhat what she would have been doing running to keep it interesting for her.
I am happy to share the routine she did if you think it might help you to pull some ideas from it. Just provide an email address.