Pond Help

Hi all, I am hoping someone out there can help me with a pond problem.
I have a family member with a pond that is about 50x20 ft and goes frome
about 4 feet to about 7 feet in depth . The pond was looking good but after
digging around the border for the installation of a waterfall the pond has
become very cloudy with the dirt that was disturbed during the installation
of that waterfall. The fish are doing fine but its very murky and its been
pumping water for months and still hasnt cleared up. I am sure if a filter
of some kind was put in use it would clear up but its not like a fishtank
I dont know what kind of filter they could install that would do the job.
Any one out there with any ideas I would greatly appreciate if you would
pass them along and when the pond thaws in the spring I will try and follow
your suggestions.....Thanks in advance Ron.