stay off the bike

As always, training for fun, and if performance comes with it, the better!
Yesterday I did 20km and today 15km easy. Also, the last 3 days I have been biking in the evening anything between 20 and 27km. I would like to rest this evening, because my training plans for the weekend are ambitious!
Do you find that swimming or other side-activities affect the quality of your training in running? Personally, if I get carried away and bike too much, the next day I can't run as hard as I'd like to.