Stuff from the trees (organic waste) and silt are two different things.
Silt is dirt, dirt don't decompose.
Organic waste comes from something that used to alive, like leaves, weeds, fish, poop, etc. This stuff breaks down over time. Breakdown time can be sped up, with some help.
You need to figure out what the stuff is, then come up with a plan.
What does it smell like?
