Unless you've had some really heavy rain and wind to stir up/bring in colloidal clay/mud, it is probably a brown algae that can look muddy. Try taking a couple water samples in clear jars....take one simply by letting the jar fill with water on top.....for the second sample, put the jar, upside down, go as deep as you can (in water not muddied by walking into the pond) and then flip the jar to fill and lift straight up and out of the water, or seal it as soon as it fills.

If both jars look equally turbid, put one jar on a someplace that gets natural daylight and put the other jar in a dark closet and do not disturb them for at least 4 days.

If both jars clear, and you have sediment on the bottom of the jar, something mechanical is muddying the pond like wind/wave action, bullhead catfish, or some sort of carp (includes Koi and goldfish)

If the jar in light does not clear, but the jar in the dark does clear, it is a brown algae which will die off on it's own when temps change.

If neither jar clears, go to any grocery store spice aisle and buy some Alum.....sprinkle in 1/2 tsp per quart, shake, and see how fast it clears.