There are some great benifits to swimming over running, and not much in the way of detractors. You're working against resistance, by pushing against the water. There isn't any impact, like there is running. Also the water cools you off, so you don't get all sweaty and nasty like running (with the added benifit of not overheating and getting heat stroke).
If you still think running is the way to go for you, go run in the pool! Try that for a few laps! Damn! The resistance of the water is pretty fierce. If you want to increase your strength running, do it in the pool. That way you're not carrying extra weight and pounding those knees, or trying to run up hills (actually up's not bad, but down really impacts hard).
Ross