I have a pond that was built 20 yrs ago. Recently I found where the riser has almost rusted off of the pipe and is leaning over and about to fall off. That doesn't concern me as much as there is a V-shaped like hole in the top of the pipe. I have bought a galvanized pipe that is split that you fold up and shove down the pipe and it will open up to try to close off the water from rushing in. It appears to me this is a temporary fix and I will have to replace the pipe real soon. Does anyone have any ideas on how I can replace the pipe and not lose too many fish?
Thanks for any suggestions.

I can't get a real picture of the situation from your post, but concrete hardens under water. Can you set some forms around the pipeing and pour in concrete to repair? Add rebar also.

How do I send pictures with a post? I have one to show what my problem is.

Look here for posting pic's:
http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=001628

Hope this helps

Still lost. Is this outside your pond, (back of the dam?) Is your riser behind the dam or in the water? Your photo looks dry to me, can't you weld on new metal?