If you have a clay bottomed pond, no funds or heavy equipment, and do have slave labor (In my case, Hunny and The Kid), this info may be helpful.
(Done for a different project described here.)
We've had topsoil flowing into our pond for the last decade. The former owner next door messed with the watershed when he filled in his small pond. Now the stockpond on the further property oveflows in heavy thunder storms, making a river overland instead of moving
underground through french drains as it was designed. Sigh.
Our pond is clay lined, cause we live in the
land of clay. The guys used a snow shovel scooper thingy (Can you tell we don't use it for snow very often?) to get sediment out of our big pond. It moves easily through the sediment. Hunny confirmed that it would be very clear if he hit the clay bottom.