My First Post on USMS

Howdy, everybody! I'm 48, as of this past Monday, and I have been getting back into shape since about Sept. of last year. Just a quick brag, I weighed 240+ back in Sept, my doctor wanted to put me on cholesterol lowering meds and my blood pressure meds were no longer doing the trick so I had to up them about 4 times until it was under control again. In two months time, I had lost 40 lbs (yes, I know that was TOO fast) but I was able to stay off the statin drugs! My other goal was to get completely off BP meds by my birthday and I did that... first time in about 11 years! It's been almost 10 months and the weight has remained between 195 to 200. I had my body fat measured at 12% a few months back but not sure if it's still that good or not but the weight is still the same. I had some surgery a month ago so I had to slow down some temporarily. I'm lifting weights every other day and currently swimming on the days in between. I had been doing my cardio on an elliptical machine but I just enjoy swimming so much that it's a hard choice. My problem is this. I want to get my heart rate up to get the most benefit from my cardio time but I seem to have a harder time of it in the pool than I do on the elliptical machine. Am I just not working hard enough or is it just harder to do in the water? I've thought about joining a Master's club because I miss the competitive aspect like I had from playing basketball for years, which was my main sport until a few years ago when I decided to give my knees and back a permanent vacation. What do you think? Could I participate successfully and just swim 2 to 3 times a week? I don't want to give up the weight either and there's only so much time in a week. Thanks in advance for your feedback!