I need help with Interval training

Well, for both swimming and running, you can do an exercise known as a ladder. In a laddder, you start with a certain distance, and keep building on it until you reach a maximum distance, and then you gradually go back down to the initial ditance. For example, with swimming, you can start with two laps, then take a break, then 3 laps, then 4 ... all the way to 10 laps without stopping. Then work your way back down. You can also do the same thing with running, by starting off with a mile, and building from there. Also, you can alternate both swimming and running, by splitting your workouts - swim a quarter of your laps (5) then run a mile, then another 5 laps, the another mile, then 5 more laps, the final mile, and then 5 laps cool down. Hope I helped and good luck with your exercise!