I experienced seeing kids only run cross country, go out for swimming, and then skip the track & field season because they did not like the track & field coach.
These swimming kids were able to run fast early in the season, get injured, and then they would catch up later after their minor injuries heal. I think that what you want to do is to do some running as part of your swimming regimen and perhaps pickup the intensity of your running as track & field approaches. If you swim twice a day why not make one of them a running workout?
Swimming can be a good cross training tool but too much of a good thing and then abruptly switching to something that is harder on the joints is not going to work.
You might also start your track & field season a bit easier than the rest of the folks. You will be ahead of those who did not run during the winter cardiovascular-wise. You could do extra work in the pool early in the season as supplementary work. Communicate this to your coach and see what he thinks. I wish that I was a better swimmer and could do it that way all year long.
Your legs do need the pounding for running, but getting away from it is good for recovery!!! Ryun, Snell, Prefontaine, Shorter, etc. did not know about recovery the way we do now. Many world class distance runners do a lot of cross training. Garrett Heath bikes, Nordic Skis, and he has spent time doing water exercises as well. He does that even when he is not injured! Heath was a multiple All-American at Stanford, still runs sub-4 minute miles, and was a state champion high school runner and skier.
It is a mistake to say that running and swimming cannot help each other. It's how we do it that matters. But be nice to your coach...communicate!!!
By the way your times show you have excellent potential as a runner. It takes time to be an "over-night sensation!"