I did the same thing Pot Luck did twice and I simply widened my pond out once. I would say the additions where I dug next to my existing pond and then cut a channel through were less stressful on the fish in that the whole pond didn't turn into chocolate milk. The last time I just widened the pond along it's whole length the entire pond turned into what looked like a sewer hole. Didn't lose a fish that I could tell. Within 3 weeks the pond cleared up to normal and everyone was happy. If you live in the North country I certainly wouldn't do this in the fall when it might freeze over while in the most turbid state. I did mine as early in the year as I could just so the algea would have a chance to grow back before winter. The algea is where you get most of the oxygen after freeze over. I too was afraid I'd kill it all but it worked.
