Silt is loose dirt that is caused by erosion. When run off water carries soil to another place that is usually undesirable it's called silt. Right now on our pond that we built last year we had silt problems in a couple small areas. We made our pond bigger last week and I'm in the process of putting up silt fences around the disturbed area of the pond. I bought them from
www.forestry-suppliers.com, but also found it locally where I got my 7.5'x120'straw mats after the fact. Since we lowered the water level while making the pond bigger I'm scooping the silt in those areas with a bucket and rope. It’s hard work now that could have been prevented, but we also where building a house at the time and something just get away from you.
Silt is also cause by the settling of muddy water in a body of water which we don’t have much of.
There are probably other causes, but those are the ones I’ve dealt with.