Without microscopically examining the water, the first guess is suspended clay particles. It could be some forms of ultra small plankton that can impart a cloudiness. Typically alum or gypsum are used to help clear ponds. Do a test on the pint of cloudy water with either gypsum or alum. Amount of alum used to prevent a fish kill depends on the alkalinity of the water. I suggest you do a search for other topics about amounts to use for alum or gypsum to clear the water. I will look for a few posts to help you with this - see below.
Bob Lusk provided this about lime and gypsum-
Aglime does no harm, at all, in ponds. It may, or may not, solve your dilemma. One thing everyone needs to remember about lime is this...when you apply it, lime has a buffering affect on the water, like Rolaids. As lime is 'absorbed', its concentration decreases. So, additional lime is needed from time to time. Lime can only raise the pH to what the pH of the lime is, and that only happens when the water is reaching saturation. Lime can be effective for water clarity, depending why the water isn't clear. But, gypsum has a different chemical reaction in water, tending to flocculate suspended solids more quickly. When it comes to clearing muddy water, I lean much closer toward gypsum than lime. If the water is acidic, lime is the best answer, for buffering.
Here are some related links:
http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=16;t=000018#000006 http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=16;t=000041#000000 http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=16;t=000014#000000 http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=001127