I add some pool workouts near the end of the season to help with the overall (upper and lower) body conditioning. Its is very demanding, however, very little pounding on the joints and I call "FREE MILES".
Why do I wait until the end of the season. Due to the fact we have already done every other thing needed for full development, ie, weights, Bounding, Plyros, Speed, Tempo, AT,....what is there left that you can throw at your body that it will respond to as a new stress....
Also, at this time of year it gives the runners something new from the same ole stuff....however, some of the same ole stuff is still needed.
This is only a suggestion, and what works for one runner (or coach) may not work well for others...that is what makes this sport so fun.