Joey, you have several options available. All the thoughts from the other guys are good. To plug the pipe will work but for how long. If it is leaking around the pipe is a different problem. You can plug the pipe and use some colored dye that will tell you where your leak is really at. If you can spend a little money, I think the best thing is to lower the level with the temporary siphon below normal pool level, then let it dry out. Then install a permanent siphon system through the dam at the water level, illustrated on
http://www.ponddampiping.com. This gives you a drain that works on its own and takes the dead water off of the bottom of the lake. You can use sdr35 pipe for your siphon system that is inexpensive. This way would require less dirt work and you keep the integrity of the dam there. You would only dig down to you desired water level. The siphon system would require at least 4' fall from the inlet to the exhaust end. Hope this helps.
