esshup has good information. Rain water rinsing down the the banks erodes or gathers surface sediment and clay into the drainage water. These fine colloidal particles due to extremely small sizes tend to settle very slowly. Certain clay soil has particles that have electrical charges the do not settle or settle very very slowly.
There are remedies for that special problem.
If you want to determine how fast your turbid pond water with suspended particulates will naturally settle,,,, collect some of the turbid water in a clear glass or plastic jar. The bigger the jar, the better the visual end results will be. 2qt jar is okay and 1 gallon+ size is better. Allow the water to sit undisturbed for 5-10 days. After several days to 2 weeks and lots of sediment is on the bottom and water is tap water clear, the pond water will naturally settle and clear up when undisturbed and shoreline is vegetated and or rock lined to minimize later full pond wind wave action and erosion. Some fish and invertebrate (animal) species can disturb bottoms sediments and create turbidity.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
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