I am 45 years old and swim 4-5 times a week. I have been swimming as my only exercise for a year or so. I have been wondering if I need to start doing some other exercises besides swimming. My main goal is just to stay in shape as I get older. I swim 2300-2600 yards and love swimming. I hate the idea of lifting weights, sounds so boring. Running is not an option due to bad knees. Is there a good reason to do something else besides swim in order to stay in shape over the long run? I only have 4-5 hours a week so I can't add weight lifting unless I dropped some swimming from my schedule. Thoughts?

It depends on how you want to stay in shape. Lifting weights will help build you muscle, and is definitely great for overall strength.

If you don't want to lift weights, try simple dryland workouts such as pushups, pullups, V-ups, etc. There are many great guides on Youtube and the internet with different core workouts. And you can usually do those in a fairly short amount of time.

I don't think you have to do any weightlifting. Swimming is good exercise by itself.

However, if you do some strength training, you'll probably find that swimming becomes easier and more fun. This is true of just about any exercise or sport. And if you do it properly, you'll lessen the likelihood of injury. You don't need to have weights to do strength training, either; you can do pushups, squats, etc using only your body weight. Right now I'm working on the one hundred pushups program (http://hundredpushups.com/) and already seeing improvement in my swimming. If you're prone to shoulder injury, take it REALLY easy, though. I'm doing each week twice.