Turbid water in an open well - What is the reason and how to get clear water from the dug well?

We have dug an open well to a depth of (10)meters. Upto 5 meters depth, its sides sealed with stone masonry and remaining  5 meters depth was dry packed with rough stones/boulders. But, since last 2years(since digging) it is oozing only turbid water having turbidity more than 100 NTU. what will be the reason and how to get clear water from this dug well.