Was this pond by any chance filled with well water? If so this looks just like a pond I just filled and in my case it's precipitated iron. If so it will settle in several days. My newly filled ponds take on a yellow brown color from the iron, then it becomes a green, then a light green, and finally crystal clear.
Alum will settle iron also although it shouldn't be necessary. (If it is indeed iron.)
I've used alum in my ponds and never had to use any lime or sodium bicabonate to stabilize the PH as my alkalinity is quite high and the ponds are well buffered.
Here's a pic of my recently filled trout pond. The color is off in the picture as it's more of a yellow/brown than green as shown here.
